Add Container Registry credential extension

[qwerty287]

From #5852

Added UI and docs.

[woodpecker-bot]

Surge PR preview deployment was removed

[codecov]

Codecov Report

❌ Patch coverage is 1.81818% with 108 lines in your changes missing coverage. Please review.
✅ Project coverage is 32.45%. Comparing base (9fb5d4d) to head (13a4e69).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
server/services/registry/with_extension.go	0.00%	60 Missing ⚠️
server/services/registry/http.go	0.00%	26 Missing ⚠️
server/services/setup.go	0.00%	9 Missing ⚠️
server/services/manager.go	0.00%	5 Missing ⚠️
server/api/repo.go	0.00%	3 Missing ⚠️
server/services/registry/combined.go	0.00%	2 Missing ⚠️
server/pipeline/create.go	0.00%	1 Missing ⚠️
server/pipeline/items.go	66.66%	1 Missing ⚠️
server/services/registry/db.go	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #5993      +/-   ##
==========================================
- Coverage   32.56%   32.45%   -0.12%     
==========================================
  Files         418      420       +2     
  Lines       28170    28268      +98     
==========================================
  Hits         9173     9173              
- Misses      18150    18248      +98     
  Partials      847      847              

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[qwerty287]

@woodpecker-ci/maintainers could I get a review here? :)