[vc-authn-oidc] Observability: Helm chart integration

[i5okie]

Description

Add native OTel configuration support to the vc-authn-oidc chart, covering both the controller (FastAPI OIDC controller) and the ACA-Py agent deployed via the acapy sub-chart.

Context

The vc-authn-oidc chart (charts/vc-authn-oidc) has two components to instrument:

1. Controller (the FastAPI OIDC controller) — templates/deployment.yaml
2. ACA-Py agent — deployed via the acapy sub-chart dependency

Use Helm's global: section so shared OTel settings are declared once and cascade to both components automatically.

Requirements

• Add a global.otel: section to values.yaml with shared fields: enabled, endpoint, protocol, tracesExporter, metricsExporter, logCorrelation
• Controller: Add otel.serviceName (local, defaults to release name); render all OTEL env vars in templates/deployment.yaml from global.otel.* (with local fallback) when global.otel.enabled is true
• ACA-Py agent: Once the acapy sub-chart has native otel: support, it will automatically inherit global.otel.* from the parent — set only acapy.otel.serviceName in the parent values.yaml

Acceptance Criteria

• Setting global.otel.enabled: true and global.otel.endpoint once results in correct env vars in both the controller pod and the aca-py pod
• Each pod has its own distinct OTEL_SERVICE_NAME
• Traces from both components appear in Tempo after deployment
• HTTP metrics from both components appear in Mimir after deployment