[PMM-13630]: Fixes service start issue + permissions issue

[maqeel75]

PMM-13630

Link to the Feature Build: SUBMODULES-0

If this PR that fixes pmm-client v3 upgrade issue that was not starting pmm-agent service and removing pmm-agent user from machine.

• API Docs updated

If this PR is related to some other PRs in this or other repositories, please provide links to those PRs:

• Links to related pull requests (optional).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 43.53%. Comparing base (b7885f1) to head (86b61c2).

Additional details and impacted files

@@            Coverage Diff             @@
##               v3    #3415      +/-   ##
==========================================
- Coverage   43.57%   43.53%   -0.04%     
==========================================
  Files         366      366              
  Lines       44238    44238              
==========================================
- Hits        19275    19259      -16     
- Misses      23275    23293      +18     
+ Partials     1688     1686       -2     

Flag	Coverage Δ
admin	11.47% <ø> (-0.05%)	⬇️
agent	51.83% <ø> (-0.13%)	⬇️
managed	45.29% <ø> (ø)
vmproxy	68.57% <ø> (ø)

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