docs(prometheus): metric name should include aws_ prefix

[samuelmasuy]

Issue

No existing issue - documentation bug fix

Description

This PR fixes incorrect metric names in the Prometheus metrics documentation. The error metrics were documented without the aws_ subsystem prefix, causing confusion when users tried to query these metrics.

Changes:

• Updated docs/guide/metrics/prometheus/index.md to correct four metric names:
  • api_call_permission_errors_total → aws_api_call_permission_errors_total
  • api_call_service_limit_exceeded_errors_total → aws_api_call_service_limit_exceeded_errors_total
  • api_call_throttled_errors_total → aws_api_call_throttled_errors_total
  • api_call_validation_errors_total → aws_api_call_validation_errors_total

Why this matters:
When users queried Prometheus using the documented metric names (without aws_ prefix), they received no results. The actual metrics exported by the controller include the aws_ subsystem prefix as defined in pkg/metrics/aws/instruments.go. This fix aligns the documentation with the actual implementation.

Checklist

• Added tests that cover your change (if possible) - N/A for documentation fix
• Added/modified documentation as required (such as the README.md, or the docs directory)
• Manually tested - verified metric names match actual Prometheus output
• Made sure the title of the PR is a good description that can go into the release notes

BONUS POINTS checklist: complete for good vibes and maybe prizes?! 🤯

• Backfilled missing tests for code in same general area 🎉
• Refactored something and made the world a better place 🌟

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: samuelmasuy
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[k8s-ci-robot]

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