Add time_slice SLO type support

[cedi]

What does this PR do?

Adds support for Datadog Time Slice SLOs alongside the existing metric and monitor SLO types.

Time Slice SLOs use an SLI specification with a metric query, a comparator, and a threshold to determine what counts as good uptime in each time window. This is modeled as a new timeSlice field on DatadogSLOSpec, following the existing pattern where each SLO type has its own dedicated payload field (query for metric, monitorIDs for monitor, timeSlice for time_slice).

The API is designed for simplicity: the user provides a single metric query string, and the operator auto-generates the named query (query1) and formula (query1) when building the Datadog API request — matching the ergonomics of metric SLOs where users provide one query and the operator handles the rest.

Example CR:

spec:
  type: time_slice
  name: my-service-availability
  timeSlice:
    query: "trace.servlet.request{env:prod}"
    comparator: ">"
    threshold: "5"
  timeframe: 7d
  targetThreshold: "97"

Motivation

The Datadog API supports three SLO types: metric, monitor, and time_slice. The operator previously only supported metric and monitor. Time Slice SLOs are useful for monitoring uptime based on SLI thresholds evaluated per time window, which is a common pattern for service availability targets.

Additional Notes

• The DataSource is intentionally omitted from the CRD and hardcoded to "metrics" in the API mapping, since Datadog only supports metric data sources for time_slice SLOs.
• The Comparator field is a kubebuilder-validated enum (>, >=, <, <=), rejected at admission time if invalid.
• Cross-field validation ensures users cannot combine incompatible fields (e.g., timeSlice with type: metric, or query with type: time_slice).
• All existing metric and monitor SLO behavior is unchanged — new types and code paths are purely additive.

Minimum Agent Versions

No minimum agent version required. This change only affects the operator's interaction with the Datadog API.

• Agent: N/A
• Cluster Agent: N/A

Describe your test plan

• Unit tests for validation (datadogslo_validation_test.go): 7 test cases covering valid time_slice spec, missing TimeSlice field, empty query, and all cross-field rejection combinations.
• Unit tests for API mapping (slo_test.go): buildSLO test cases covering metric, monitor, and time_slice — verifying the full SDK object construction including hardcoded data source and auto-generated query/formula names.
• All existing tests continue to pass unchanged.

Checklist

• PR has at least one valid label: bug, enhancement, refactoring, documentation, tooling, and/or dependencies
• PR has a milestone or the qa/skip-qa label
• All commits are signed (see: signing commits)

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 38.90%. Comparing base (7fae85c) to head (0f8996a).
⚠️ Report is 25 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2701      +/-   ##
==========================================
+ Coverage   38.80%   38.90%   +0.10%     
==========================================
  Files         309      309              
  Lines       26750    26775      +25     
==========================================
+ Hits        10379    10416      +37     
+ Misses      15592    15586       -6     
+ Partials      779      773       -6     

Flag	Coverage Δ
unittests	38.90% <100.00%> (+0.10%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Files with missing lines	Coverage Δ
internal/controller/datadogslo/slo.go	80.58% <100.00%> (+21.60%)	⬆️

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