[mediator-credo] Observability: Helm chart integration

[i5okie]

Description

Add native OTel configuration support to the didcomm-mediator-credo chart in the OWF helm-charts repo.

Context

The deployment chart is at charts/didcomm-mediator-credo/. The deployment template accepts arbitrary env vars via {{- toYaml .Values.environment }}, which is flexible but not a native otel: integration. DITP gitops per-env overrides live in services/mediator-credo/charts/{env}/values.yaml.

Requirements

• Add a native otel: section to values.yaml with fields: enabled, endpoint, protocol, tracesExporter, metricsExporter, serviceName
• Support global.otel.* for all shared fields (prefer global with local fallback), consistent with the pattern used across all other services
• Render OTEL env vars conditionally in templates/deployment.yaml when otel.enabled (or global.otel.enabled) is true, replacing reliance on the generic environment passthrough for OTel config

Acceptance Criteria

• Setting global.otel.enabled: true and global.otel.endpoint in the gitops values.yaml results in correct env vars in the deployed pod
• Traces appear in Tempo after deployment
• HTTP metrics appear in Mimir after deployment