.Net: Added Labels field in Gemini Request. (#12300)

### Motivation and Context

### Description
Added `Labels` field in Gemini Request.

### Contribution Checklist

- [Y] The code builds clean without any errors or warnings
- [Y] The PR follows the [SK Contribution
Guidelines](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md)
and the [pre-submission formatting
script](https://github.com/microsoft/semantic-kernel/blob/main/CONTRIBUTING.md#development-scripts)
raises no violations
- [Y] All unit tests pass, and I have added new tests where possible
- [Y] I didn't break anyone 😄

Fixes #12257

---------

Co-authored-by: Adit Sheth <adsheth@microsoft.com>

Author: shethaadit

dotnet/src/Connectors/Connectors.Google.UnitTests/Core/Gemini/GeminiRequestTests.cs

@@ -521,6 +521,24 @@ public void CachedContentFromPromptReturnsAsExpected()
         Assert.Equal(executionSettings.CachedContent, request.CachedContent);
     }
 
+    [Fact]
+    public void LabelsFromPromptReturnsAsExpected()
+    {
+        // Arrange
+        var prompt = "prompt-example";
+        var executionSettings = new GeminiPromptExecutionSettings
+        {
+            Labels = "Key1:Value1"
+        };
+
+        // Act
+        var request = GeminiRequest.FromPromptAndExecutionSettings(prompt, executionSettings);
+
+        // Assert
+        Assert.NotNull(request.Configuration);
+        Assert.Equal(executionSettings.Labels, request.Labels);
+    }
+
     [Fact]
     public void CachedContentFromChatHistoryReturnsAsExpected()
     {
@@ -541,6 +559,26 @@ public void CachedContentFromChatHistoryReturnsAsExpected()
         Assert.Equal(executionSettings.CachedContent, request.CachedContent);
     }
 
+    [Fact]
+    public void LabelsFromChatHistoryReturnsAsExpected()
+    {
+        // Arrange
+        ChatHistory chatHistory = [];
+        chatHistory.AddUserMessage("user-message");
+        chatHistory.AddAssistantMessage("assist-message");
+        chatHistory.AddUserMessage("user-message2");
+        var executionSettings = new GeminiPromptExecutionSettings
+        {
+            Labels = "Key1:Value1"
+        };
+
+        // Act
+        var request = GeminiRequest.FromChatHistoryAndExecutionSettings(chatHistory, executionSettings);
+
+        // Assert
+        Assert.Equal(executionSettings.Labels, request.Labels);
+    }
+
     [Fact]
     public void ResponseSchemaConvertsNullableTypesToOpenApiFormat()
     {

dotnet/src/Connectors/Connectors.Google.UnitTests/Services/GoogleAIGeminiChatCompletionServiceTests.cs

@@ -69,6 +69,35 @@ public async Task RequestCachedContentWorksCorrectlyAsync(string? cachedContent)
         }
     }
 
+    [Theory]
+    [InlineData(null)]
+    [InlineData("key:value")]
+    [InlineData("")]
+    public async Task RequestLabelsWorksCorrectlyAsync(string? labels)
+    {
+        // Arrange
+        string model = "fake-model";
+        var sut = new GoogleAIGeminiChatCompletionService(model, "key", httpClient: this._httpClient);
+
+        // Act
+        var result = await sut.GetChatMessageContentAsync("my prompt", new GeminiPromptExecutionSettings { Labels = labels });
+
+        // Assert
+        Assert.NotNull(result);
+        Assert.NotNull(this._messageHandlerStub.RequestContent);
+
+        var requestBody = UTF8Encoding.UTF8.GetString(this._messageHandlerStub.RequestContent);
+        if (labels is not null)
+        {
+            Assert.Contains($"\"labels\":\"{labels}\"", requestBody);
+        }
+        else
+        {
+            // Then no quality is provided, it should not be included in the request body
+            Assert.DoesNotContain("labels", requestBody);
+        }
+    }
+
     [Theory]
     [InlineData(null, false)]
     [InlineData(0, true)]

dotnet/src/Connectors/Connectors.Google.UnitTests/Services/VertexAIGeminiChatCompletionServiceTests.cs

@@ -80,6 +80,35 @@ public async Task RequestCachedContentWorksCorrectlyAsync(string? cachedContent)
         }
     }
 
+    [Theory]
+    [InlineData(null)]
+    [InlineData("key:value")]
+    [InlineData("")]
+    public async Task RequestLabelsWorksCorrectlyAsync(string? labels)
+    {
+        // Arrange
+        string model = "fake-model";
+        var sut = new GoogleAIGeminiChatCompletionService(model, "key", httpClient: this._httpClient);
+
+        // Act
+        var result = await sut.GetChatMessageContentAsync("my prompt", new GeminiPromptExecutionSettings { Labels = labels });
+
+        // Assert
+        Assert.NotNull(result);
+        Assert.NotNull(this._messageHandlerStub.RequestContent);
+
+        var requestBody = UTF8Encoding.UTF8.GetString(this._messageHandlerStub.RequestContent);
+        if (labels is not null)
+        {
+            Assert.Contains($"\"labels\":\"{labels}\"", requestBody);
+        }
+        else
+        {
+            // Then no quality is provided, it should not be included in the request body
+            Assert.DoesNotContain("labels", requestBody);
+        }
+    }
+
     [Theory]
     [InlineData(null, false)]
     [InlineData(0, true)]

dotnet/src/Connectors/Connectors.Google/Core/Gemini/Models/GeminiRequest.cs

@@ -46,6 +46,10 @@ internal sealed class GeminiRequest
     [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
     public string? CachedContent { get; set; }
 
+    [JsonPropertyName("labels")]
+    [JsonIgnore(Condition = JsonIgnoreCondition.WhenWritingNull)]
+    public string? Labels { get; set; }
+
     public void AddFunction(GeminiFunction function)
     {
         // NOTE: Currently Gemini only supports one tool i.e. function calling.
@@ -430,6 +434,7 @@ private static void AddSafetySettings(GeminiPromptExecutionSettings executionSet
     private static void AddAdditionalBodyFields(GeminiPromptExecutionSettings executionSettings, GeminiRequest request)
     {
         request.CachedContent = executionSettings.CachedContent;
+        request.Labels = executionSettings.Labels;
         if (executionSettings.ThinkingConfig is not null)
         {
             request.Configuration ??= new ConfigurationElement();

dotnet/src/Connectors/Connectors.Google/GeminiPromptExecutionSettings.cs

@@ -28,6 +28,7 @@ public sealed class GeminiPromptExecutionSettings : PromptExecutionSettings
     private string? _responseMimeType;
     private object? _responseSchema;
     private string? _cachedContent;
+    private string? _labels;
     private IList<GeminiSafetySetting>? _safetySettings;
     private GeminiToolCallBehavior? _toolCallBehavior;
     private GeminiThinkingConfig? _thinkingConfig;
@@ -147,6 +148,22 @@ public IList<GeminiSafetySetting>? SafetySettings
         }
     }
 
+    /// <summary>
+    /// Gets or sets the labels.
+    /// </summary>
+    /// <value>
+    /// Metadata that can be added to the API call in the format of key-value pairs.
+    /// </value>
+    public string? Labels
+    {
+        get => this._labels;
+        set
+        {
+            this.ThrowIfFrozen();
+            this._labels = value;
+        }
+    }
+
     /// <summary>
     /// Gets or sets the behavior for how tool calls are handled.
     /// </summary>