apis: add extension plugin framework for PodMetric

[jasonliu747]

Signed-off-by: Jason Liu jasonliu747@gmail.com

Ⅰ. Describe what this PR does

Ⅱ. Does this pull request fix one issue?

Ⅲ. Describe how to verify it

Ⅳ. Special notes for reviews

V. Checklist

• I have written necessary docs and comments
• I have added necessary unit tests and integration tests
• All checks passed in make test

[codecov]

Codecov Report

Base: 66.99% // Head: 66.97% // Decreases project coverage by -0.02% ⚠️

Coverage data is based on head (d738c3f) compared to base (fd4432b).
Patch has no changes to coverable lines.

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #955      +/-   ##
==========================================
- Coverage   66.99%   66.97%   -0.03%     
==========================================
  Files         243      243              
  Lines       28166    28166              
==========================================
- Hits        18871    18865       -6     
- Misses       8008     8012       +4     
- Partials     1287     1289       +2     

Flag	Coverage Δ
unittests	66.97% <ø> (-0.03%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
pkg/util/httputil/reverseproxy.go	84.30% <0.00%> (-1.60%)	⬇️

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[saintube]

/lgtm

[saintube]

/lgtm

[hormes]

/approve

[koordinator-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: hormes

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Needs approval from an approver in each of these files:

• apis/OWNERS [hormes]
• config/OWNERS [hormes]

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