feat: add support for configuring push/remote mirrors

[amimas]

This change adds support for managing/configuring push mirrors in GitLab. The change includes necessary acceptance tests and documentation.

Note: GitLab currently has a limitation in their API for configuring SSH based mirrors. For this type of mirror, GitLab needs to know the "host key" of the target system. This option can only be configured when setting up the mirror manually using the UI. Due to lack of API options in GitLab side, SSH based mirror setup will not be functional.

resolves #873

[codecov]

Codecov Report

❌ Patch coverage is 92.59259% with 10 lines in your changes missing coverage. Please review.
✅ Project coverage is 88.54%. Comparing base (230c16a) to head (602229e).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
...orm/processors/project/remote_mirrors_processor.py	92.53%	10 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main    #1157       +/-   ##
===========================================
+ Coverage   61.55%   88.54%   +26.98%     
===========================================
  Files          73       74        +1     
  Lines        3470     3605      +135     
===========================================
+ Hits         2136     3192     +1056     
+ Misses       1334      413      -921     

Flag	Coverage Δ
integration	87.18% <92.59%> (+28.59%)	⬆️
unittests	37.69% <15.55%> (-0.87%)	⬇️

Files with missing lines	Coverage Δ
gitlabform/processors/project/__init__.py	100.00% <100.00%> (ø)
...orm/processors/project/remote_mirrors_processor.py	92.53% <92.53%> (ø)

... and 41 files with indirect coverage changes

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