[master] Add missing kubeproxy extra env and mounts

[Oats87]

Forwardport to master:

• [release-1.21] Add missing kubeproxy extra env and mounts #1625
• Allow customizing of the static pod manifests for CPU, files, and directories #1233

[codecov-commenter]

Codecov Report

Merging #1626 (e8d9460) into master (6396cef) will decrease coverage by 0.00%.
The diff coverage is 0.00%.

@@            Coverage Diff            @@
##           master   #1626      +/-   ##
=========================================
- Coverage    7.78%   7.77%   -0.01%     
=========================================
  Files          21      21              
  Lines        1863    1865       +2     
=========================================
  Hits          145     145              
- Misses       1696    1698       +2     
  Partials       22      22              

Flag	Coverage Δ
unittests	7.77% <0.00%> (-0.01%)	⬇️

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Impacted Files	Coverage Δ
pkg/rke2/rke2_linux.go	0.00% <0.00%> (ø)

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