Add metrics handling and update architecture documentation

docs/ARCHITECTURE.md

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+# StreamPay Backend Architecture
+
+This document provides an overview of the StreamPay backend architecture, its components, and the data flow for key operations.
+
+## Components
+
+The backend is composed of the following main components:
+
+- **HTTP API:** A public-facing API for managing streams, metering, and settlements.
+- **Workers:** Background services for handling asynchronous tasks like event ingestion and processing.
+- **Database:** A PostgreSQL database for storing stream data, account information, and other persistent data.
+- **Redis:** An in-memory data store for caching and managing distributed locks.
+- **RPC Clients:** Clients for interacting with blockchain nodes for on-chain operations.
+
+## Data Flow
+
+### Stream Settlement
+
+The following diagram illustrates the data flow for stream settlement:
+
+```mermaid
+graph TD
+    subgraph "External Systems"
+        A[Indexer]
+    end
+
+    subgraph "StreamPay Backend"
+        B[HTTP API]
+        C[Event Ingestion Service]
+        D[Database]
+        E[Settlement Service]
+        F[RPC Client]
+    end
+
+    subgraph "Blockchain"
+        G[Smart Contract]
+    end
+
+    A -- Webhook --> C
+    C -- Validated Event --> D
+    B -- Settlement Request --> E
+    E -- Reads Stream Data --> D
+    E -- Executes Settlement --> F
+    F -- Interacts with --> G
+```
+
+**Steps:**
+
+1. The **Indexer** sends a webhook to the **Event Ingestion Service** when a stream is created or updated.
+2. The **Event Ingestion Service** validates the webhook and stores the event data in the **Database**.
+3. A user initiates a settlement through the **HTTP API**.
+4. The **Settlement Service** reads the stream data from the **Database**.
+5. The **Settlement Service** uses the **RPC Client** to execute the settlement on the blockchain.
+6. The **RPC Client** interacts with the **Smart Contract** to perform the settlement.