add support to merge system CA with PMG CA

[Sahilb315]

Fixes #167

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[safedep]

SafeDep Report Summary

No dependency changes detected. Nothing to scan.

_{This report is generated by SafeDep Github App}

[codecov-commenter]

Codecov Report

❌ Patch coverage is 77.66990% with 23 lines in your changes missing coverage. Please review.
✅ Project coverage is 41.05%. Comparing base (b0305cb) to head (08b00b4).

Files with missing lines	Patch %	Lines
proxy/certmanager/generator.go	78.43%	14 Missing and 8 partials ⚠️
internal/flows/proxy_flow.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #169      +/-   ##
==========================================
+ Coverage   40.30%   41.05%   +0.74%     
==========================================
  Files          87       87              
  Lines        5500     5602     +102     
==========================================
+ Hits         2217     2300      +83     
- Misses       3084     3096      +12     
- Partials      199      206       +7     

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