feat(cache): add ECR support for layer caching in buildkit

[argoyle]

Introduce configuration options for AWS ECR as a remote layer cache
backend in buildkit builds. Update the documentation and code to
support caching layer configuration, improve build speed, and allow
for better management of build artifacts.

[peter-svensson]

Didn't find a test for the case when someone tries to configure:

cache:
  gitlab:
    url: ...

Not something we support but how will the error message look like?

[codecov]

Codecov Report

❌ Patch coverage is 83.73984% with 20 lines in your changes missing coverage. Please review.
✅ Project coverage is 90.65%. Comparing base (b1293c8) to head (1699d4b).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
pkg/build/build.go	70.58%	14 Missing and 1 partial ⚠️
pkg/docker/auth.go	87.50%	3 Missing and 2 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1329      +/-   ##
==========================================
- Coverage   91.02%   90.65%   -0.38%     
==========================================
  Files          38       38              
  Lines        1683     1787     +104     
==========================================
+ Hits         1532     1620      +88     
- Misses         94      107      +13     
- Partials       57       60       +3     

Flag	Coverage Δ
unittests	90.65% <83.73%> (-0.38%)	⬇️

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[argoyle]

Didn't find a test for the case when someone tries to configure:

cache:
  gitlab:
    url: ...

Not something we support but how will the error message look like?

Like this:

yaml: unmarshal errors:
  line 19: field gitlab not found in type config.CacheConfig