Read Prometheus key/cert from memory

[jjngx]

Proposed changes

This PR addresses the following:

• cert and key files for metrics server are not stored on container's FS (I/O ops is eliminated)
• tls cert for metrics server is created immediately from prometheus k8s cert when the metrics server starts
• the mechanism is exactly the same as introduced in the service insight server

Tested manually on a local kind cluster.
Existing Python integration tests cover the functionality.

Checklist

Before creating a PR, run through this checklist and mark each as complete.

• I have read the CONTRIBUTING doc
• I have added tests that prove my fix is effective or that my feature works
• I have checked that all unit tests pass after adding my changes
• I have updated necessary documentation
• I have rebased my branch onto main
• I will ensure my PR is targeting the main branch and pulling from my branch from my own fork

[github-actions]

Dependency Review

✅ No vulnerabilities or license issues found.

Scanned Manifest Files

[codecov]

Codecov Report

Merging #4023 (7050689) into main (6ce07ed) will increase coverage by 0.02%.
The diff coverage is n/a.

❗ Current head 7050689 differs from pull request most recent head b8bf859. Consider uploading reports for the commit b8bf859 to get more accurate results

@@            Coverage Diff             @@
##             main    #4023      +/-   ##
==========================================
+ Coverage   51.83%   51.85%   +0.02%     
==========================================
  Files          59       59              
  Lines       16705    16705              
==========================================
+ Hits         8659     8663       +4     
+ Misses       7747     7745       -2     
+ Partials      299      297       -2     

see 1 file with indirect coverage changes

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