Add otel logging core to clean-nfs-cache job

[djeebus]

Note

Adds optional OpenTelemetry logging to clean-nfs-cache with a new --otel-collector-endpoint flag and Nomad wiring from secret, plus minor refactors.

• Orchestrator (clean-nfs-cache):
  • OTel logging: Integrates OTel log core (resource, OTLP gRPC exporter) and supports --otel-collector-endpoint flag; logger initialized with optional OTel core.
  • Refactors: rename results.union to results.sum; simplify deletion logging; remove unused size-formatting and usage logs.
  • Constants: introduce serviceVersion, commitSHA, and serviceName grouping.
  • Deps: promote go.opentelemetry.io/otel/exporters/otlp/otlplog/otlploggrpc to direct dependency.
• IaC/Nomad:
  • Pass otel_collector_endpoint from google_secret_manager_secret_version.grafana_logs_url into job template and conditionally append CLI arg in jobs/clean-nfs-cache.hcl.

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