feat(observability): deploy configs as GHCR image via init container

[Mohith1612]

Summary

• Adds Dockerfile.observability-configs — a minimal Alpine image that packages all Prometheus, OTel Collector, Tempo, Loki, Promtail, and Grafana config files from observability/
• Replaces the scp-based config transfer with a configs-init init container in the VM compose: docker compose pull fetches the configs image from GHCR alongside api/worker, and docker compose up runs it first to populate a named volume before the observability services start
• Deploy script stays unchanged — same docker compose pull + up pattern as before

How it works

docker compose pull        # fetches api, worker, observability-configs + sidecar images
docker compose up -d       # runs configs-init → populates volume → starts all services

configs-init exits after copying, all other observability services depend on service_completed_successfully.

Test plan

• CI passes and all three images build successfully (api, worker, observability-configs)
• After merge: deploy-backend job succeeds
• On VM: docker compose ps shows configs-init as exited (0) and all other services healthy
• Grafana dashboards load at grafana.mohith16.com