Observability Phase 1 - Foundations: Propagation + basic logs

[david-martin]

Jira: https://issues.redhat.com/browse/CONNLINK-506

Implement foundational otel integration as per the observability plan in #350

• Pick observability backend(s): OTLP -> Collector -> Tempo/Jaeger + Prometheus + Loki.
• Enable trace context propagation everywhere (Envoy -> ext-proc -> broker -> servers).
• Turn on Envoy JSON access logs with trace_id, response_code_details, upstream cluster.
• Switch MCP Router + MCP Broker to structured logs with trace_id.
• Integration story with Kiali

Outcome: Gives immediate value: you can already find “who emitted the 404”.

For reference, foundational changes to use otel in the kuadrant operator Kuadrant/kuadrant-operator#1670

[esnible]

We might want to break this down into two pieces: observability foundations for the dev environment make target, and observability foundations for users who don't use our cluster setup.

FYI Note that https://github.com/kagenti/kagenti 's dev environment already installed and configures Kiali, for use with MCP-Gateway.