feat(ext_proc): add support for observability mode

[lboynton]

What this PR does / why we need it:

Which issue(s) this PR fixes:

Fixes #

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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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[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 75.58%. Comparing base (69e072f) to head (ddaf0d7).
⚠️ Report is 7 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #9461      +/-   ##
==========================================
+ Coverage   75.34%   75.58%   +0.23%     
==========================================
  Files         252      252              
  Lines       41492    41850     +358     
==========================================
+ Hits        31263    31633     +370     
+ Misses       8116     8088      -28     
- Partials     2113     2129      +16     

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