feat: expose provider metrics in the Helm chart

[charleswool]

Description

Exposes the provider's Prometheus /metrics endpoint through the Helm chart.

Note

Stacked on #2847, which adds the --enable-metrics / --metrics-port flags to the provider. This branch contains that commit, so review the chart commit here; please merge #2847 first and I'll rebase onto main afterward.

Change

• Pass --enable-metrics and --metrics-port to the provider when metrics.enabled is true (matching the v1 flag convention).
• Add the metrics container port (metrics, default 8888).
• Add prometheus.io/{scrape,port,path} pod annotations for annotation-based Prometheus scraping.
• New metrics values: enabled (default true) and port (default 8888), documented in the chart README.

A Prometheus Operator PodMonitor was split out of this PR per review feedback and will follow separately.

Testing

helm template verified:

• default (metrics.enabled=true): --enable-metrics + --metrics-port=8888, the metrics container port, and the scrape annotations are rendered.
• metrics.enabled=false: none of the above are rendered.
• --set-string metrics.port=9999: the port still renders as an integer (| int).

[Copilot]

Pull request overview

This PR updates the ratify-gatekeeper-provider Helm chart to expose the provider’s Prometheus /metrics endpoint via pod annotations and an optional Prometheus Operator PodMonitor, and wires the configured metrics port into the provider container args.

Changes:

• Add new metrics values (enabled, port, podMonitor.*) and document them in the chart README.
• Add conditional Prometheus scrape annotations and a named metrics container port to the provider Deployment.
• Add an optional PodMonitor template for Prometheus Operator-based scraping.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
deployments/ratify-gatekeeper-provider/values.yaml	Introduces default metrics configuration values (enabled/port/PodMonitor settings).
deployments/ratify-gatekeeper-provider/templates/deployment.yaml	Adds scrape annotations, passes --metrics-port, and conditionally exposes the metrics container port.
deployments/ratify-gatekeeper-provider/templates/podmonitor.yaml	Adds an optional Prometheus Operator PodMonitor for scraping /metrics.
deployments/ratify-gatekeeper-provider/README.md	Documents the new metrics-related chart values.

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.63%. Comparing base (52e0867) to head (9a35e76).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2848      +/-   ##
==========================================
+ Coverage   76.58%   76.63%   +0.05%     
==========================================
  Files          89       89              
  Lines        4095     4104       +9     
==========================================
+ Hits         3136     3145       +9     
  Misses        812      812              
  Partials      147      147              

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[charleswool]

CI fix: the e2e helm install was timing out because the chart passes --metrics-port to the provider, but this PR was branched off main where that flag does not exist yet (it is added in #2847), so the container crashed on the unknown flag and the pod never became Ready. Rebuilt this branch stacked on #2847 so the built image supports the flag. Please merge #2847 first; I will rebase onto main after it lands.