fix: add Prometheus scraping for the STAC service

[komalRay]

Summary

Add optional Prometheus scraping support for the eoAPI STAC service in the Helm chart.

This change supports the OpenAerialMap v2 observability work by allowing the STAC service to expose its /metrics endpoint and by generating a Prometheus Operator ServiceMonitor for it.

Monitoring remains disabled by default and must be explicitly enabled.

Changes

• Add STAC monitoring configuration to the Helm chart.
• Add optional Prometheus ServiceMonitor generation.
• Configure the monitor to:
  • Target the STAC Kubernetes service.
  • Scrape the named http service port.
  • Use the /metrics path.
  • Use a configurable scrape interval.
• Add Helm tests covering the generated STAC monitoring configuration.
• Preserve existing behavior when monitoring is disabled.

OpenAerialMap Context

This is the infrastructure portion of the first observability increment for OpenAerialMap v2.

The related OAM application change adds Prometheus instrumentation to the STAC API and exposes /metrics when enabled. This PR adds the Kubernetes chart configuration needed for Prometheus Operator discovery and scraping.

Related application repository:

https://github.com/hotosm/openaerialmap

Related OAM issue:

Validation

The chart and integration were validated locally using a Kubernetes cluster with Prometheus support.

Validated:

• Helm chart renders successfully with monitoring disabled.
• No ServiceMonitor is generated when monitoring is disabled.
• Helm chart renders successfully with STAC monitoring enabled.
• The generated ServiceMonitor selects the STAC service.
• The generated ServiceMonitor uses the named http port.
• The scrape path is /metrics.
• The scrape interval is configurable.
• The STAC service exposes /metrics when Prometheus monitoring is enabled.
• Prometheus discovers the STAC target.
• Prometheus reports the target as healthy with up = 1.
• Request metrics are visible in Prometheus after generating STAC traffic.
• Helm tests cover the generated STAC monitoring configuration.

Scope

This PR does not include:

• OpenTelemetry tracing.
• Sentry integration.
• TiTiler instrumentation.
• Instrumentation for other OAM v2 services.
• Grafana dashboard creation.
• Production deployment changes.

Those should be handled as follow-up work.

Checklist

• I have tested the changes locally.
• I have added or updated Helm tests where appropriate.
• I have kept monitoring opt-in by default.
• I have avoided unrelated changes.
• Documentation updates are required.
• Production rollout is required.

[pantierra]

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