Migrate trace observer to use OpenChoreo observer instead of OpenSearch directly

[AnoshanJ]

Summary

The agent manager service currently integrates with a standalone trace observer service (clients/traceobserversvc/) for fetching agent traces. This should be migrated to use the OpenChoreo observer instead, aligning with the broader OpenChoreo platform observability stack.

Current State

• Client: agent-manager-service/clients/traceobserversvc/
• Config: TraceObserverConfig with a URL field
• Used in: services/observability_manager.go via TraceObserverClient interface (ListTraces, ExportTraces, TraceDetailsById)

What needs to change

• Replace traceobserversvc client with an OpenChoreo observer client
• Update config (TraceObserverConfig → OpenChoreo observer config)
• Update observability_manager.go to use the new client
• Update wiring (wiring/wire.go, wiring/wire_gen.go)
• Update mocks and tests
• Update Helm chart values to point to the OpenChoreo observer endpoint

Why

Consolidates observability onto the OpenChoreo platform, removing the need for a separate trace observer deployment.