Add ext_authz metrics to envoy integration

[Kaycell]

What does this PR do?

I've observed we are missing metrics from envoy ext_authz http filters. Documentation
Also the failure_mode_allowed is missing for the rate limit filter even the other metrics are present Documentation

Motivation

Gathering a broader set of metrics

Additional Notes

Review checklist (to be filled by reviewers)

• Feature or bugfix MUST have appropriate tests (unit, integration, e2e)
• PR title must be written as a CHANGELOG entry (see why)
• Files changes must correspond to the primary purpose of the PR as described in the title (small unrelated changes should have their own PR)
• PR must have changelog/ and integration/ labels attached

[codecov]

Codecov Report

Merging #12374 (2f2dda8) into master (f245e7c) will not change coverage.
The diff coverage is n/a.

Flag	Coverage Δ
envoy	94.02% <ø> (ø)

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[ofek]

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