refactor: Removed nginx and refactors imports

[frgfm]

This PR introduces the following modifications:

• removes nginx since it was bypassed
• refactors all imports and project hierarchy
• updates labeler & test accordingly

[codecov]

Codecov Report

Merging #239 (fa321f9) into main (f88dbbf) will increase coverage by 0.29%.
The diff coverage is 96.37%.

@@            Coverage Diff             @@
##             main     #239      +/-   ##
==========================================
+ Coverage   92.35%   92.64%   +0.29%     
==========================================
  Files          50       61      +11     
  Lines        1386     1442      +56     
==========================================
+ Hits         1280     1336      +56     
  Misses        106      106              

Flag	Coverage Δ
client	69.07% <ø> (ø)
unittests	94.34% <96.37%> (+0.24%)	⬆️

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Impacted Files	Coverage Δ
src/app/schemas/__init__.py	100.00% <ø> (ø)
src/app/schemas/alerts.py	100.00% <ø> (ø)
src/app/schemas/base.py	100.00% <ø> (ø)
src/app/schemas/groups.py	100.00% <ø> (ø)
src/app/schemas/installations.py	100.00% <ø> (ø)
src/app/schemas/webhooks.py	100.00% <ø> (ø)
src/app/models/webhook.py	90.00% <90.00%> (ø)
src/app/models/group.py	91.66% <91.66%> (ø)
src/app/models/user.py	93.33% <93.33%> (ø)
src/app/models/installation.py	94.44% <94.44%> (ø)
... and 35 more

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