feat(telemetry): add prefix support for opentelemetry metrics

[gray-oni]

What this PR does / why we need it:

feat(telemetry): add a new field to opentelemetry sink

This PR adds prefix field to opentelemetry sink settings. So an end-user can setup their envoy metrics with a custom prefix.

Which issue(s) this PR fixes:

Fixes #6859

Example

spec:
  telemetry:
    metrics:
      sinks:
        - type: OpenTelemetry
          openTelemetry:
            host: otel-collector.example.com
            port: 4317
            reportHistogramsAsDeltas: true
            reportCountersAsDeltas: true
            prefix: envoy

---

PR Checklist

• Authorship & ownership: Coding agents / AI assistants are welcome, but I have reviewed every change, understand how and why it works, can explain and maintain it, and take full responsibility for this PR. I have not submitted generated output I do not understand.
• DCO: All commits are signed off (git commit -s). See DCO: Sign your work.
• API agreed first: If this PR contains API changes (changes under /api), the API was discussed and agreed before the implementation. The API change can be in a separate PR, or in the same PR, but the API must be agreed before implementation. N/A if this PR does not contain API changes.
• Required checks pass: make generate gen-check, make lint, and the unit-test/coverage build pass. (Flaky e2e failures are not considered breakages, but gen-check, lint, and coverage MUST pass.)
• Tests added/updated: New/changed code is covered by appropriate tests. N/A if this PR does not contain code changes.
• Docs: User-facing changes update the docs, either in this PR or a follow-up PR. N/A if this PR does not contain user-facing changes.
• Release notes: For any non-trivial change, added a release-note fragment under release-notes/current/<section>/<pr-number>-<slug>.md (see release-notes/current/README.md for sections and naming). N/A if this PR does not contain non-trivial changes.
• Generated files committed: Ran make gen-check and committed the result if API/helm charts/modules changed.
• Scope & compatibility: The PR is reasonably scoped (no unrelated changes) and preserves backward compatibility, or any breaking change is called out above and documented in release-notes/current/breaking_changes/.
• Codex review: Requested a Codex review and addressed all of its comments.
• Copilot review: Requested a Copilot review and addressed all of its comments.

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[chatgpt-codex-connector]

💡 Codex Review

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Reviewed commit: 4acb00d89f

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[gray-oni]

@codex

[chatgpt-codex-connector]

💡 Codex Review

Here are some automated review suggestions for this pull request.

Reviewed commit: 7335aa453d

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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.34%. Comparing base (e56c0ff) to head (3b7fd17).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9720      +/-   ##
==========================================
+ Coverage   81.32%   81.34%   +0.01%     
==========================================
  Files         264      264              
  Lines       40964    40969       +5     
==========================================
+ Hits        33315    33326      +11     
+ Misses       7648     7642       -6     
  Partials        1        1              

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[gray-oni]

Hi @zirain, I've seen you in the original issue discussion section. What could be the next steps for me to move forward with this change?

[gray-oni]

It looks like some test suites are flaky and not representative

[gray-oni]

/retest

[gray-oni]

Tests are green. ready for review🙂

[zirain]

can we have a e2e for this?

[gray-oni]

hey @zirain ,Thanks, an e2e test was added

[arkodg]

@gray-oni can you make generate again and commit those changes

[gray-oni]

@arkodg done, only make manifests had a drift, included in af7fc2f

[gray-oni]

hey @zirain, I had to resolve conflicts with main. could you trigger CI and re-approve PR if everything looks good?

[gray-oni]

/retest

[zirain]

/retest