Add registry callback support

[ruksi]

Support for receiving signed URLs that allow getting Docker registry credentials later.

[codecov-commenter]

Codecov Report

Merging #4 into master will increase coverage by 1.31%.
The diff coverage is 96.07%.

@@            Coverage Diff             @@
##           master       #4      +/-   ##
==========================================
+ Coverage   95.37%   96.69%   +1.31%     
==========================================
  Files          10       15       +5     
  Lines         173      242      +69     
  Branches       11       13       +2     
==========================================
+ Hits          165      234      +69     
  Misses          5        5              
  Partials        3        3              

Impacted Files	Coverage Δ
laituri_tests/test_docker_v1.py	91.66% <91.66%> (ø)
laituri/docker/credential_manager/__init__.py	100.00% <100.00%> (ø)
...i/docker/credential_manager/credential_managers.py	100.00% <100.00%> (ø)
laituri/docker/credential_manager/docker_v1.py	100.00% <100.00%> (ø)
...ential_manager/registry_credentials_callback_v1.py	100.00% <100.00%> (ø)
laituri/utils/retry.py	100.00% <100.00%> (ø)
laituri_tests/mock_data.py	100.00% <100.00%> (ø)
laituri_tests/test_credential_managers.py	100.00% <100.00%> (+6.89%)	⬆️
...uri_tests/test_registry_credentials_callback_v1.py	100.00% <100.00%> (ø)
... and 4 more

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