feat: added support for changing config via API

[eusebiu-constantin-petu-dbk]

closes #268, closes #698

Signed-off-by: Petu Eusebiu [email protected]

What does this PR do / Why do we need it:

• added a http handler to GET current zot config or POST a new one

• only admins can GET/POST configs

• ~~after zot successfully starts its server it will back up the current configuration~~

• after a POST config, zot will validate it and restart the server with the new configuration ~~if the server crashes because of config errors zot will restore the config to the last backup.~~ (not anymore)

• the config file which zot starts with is the single source of configuration and it will always reflect the current configuration of a running zot.

By submitting this pull request, I confirm that my contribution is made under the terms of the Apache 2.0 license.

[codecov[bot]]

Codecov Report

Merging #729 (8efbe56) into main (2d877aa) will increase coverage by 0.10%. The diff coverage is 94.91%.

@@            Coverage Diff             @@
##             main     #729      +/-   ##
==========================================
+ Coverage   88.75%   88.85%   +0.10%     
==========================================
  Files          73       77       +4     
  Lines       13847    14009     +162     
==========================================
+ Hits        12290    12448     +158     
- Misses       1212     1215       +3     
- Partials      345      346       +1     

Impacted Files	Coverage Δ
pkg/api/config/config.go	88.57% <ø> (-0.66%)	:arrow_down:
pkg/api/authn.go	85.71% <50.00%> (ø)
pkg/cli/root.go	88.80% <72.41%> (-6.63%)	:arrow_down:
pkg/cli/config_reloader.go	81.01% <80.95%> (-0.24%)	:arrow_down:
pkg/api/config/loader.go	92.00% <92.00%> (ø)
pkg/api/authz.go	98.40% <100.00%> (+0.08%)	:arrow_up:
pkg/api/config/validator.go	100.00% <100.00%> (ø)
pkg/api/controller.go	92.72% <100.00%> (-0.24%)	:arrow_down:
pkg/api/routes.go	96.83% <100.00%> (+<0.01%)	:arrow_up:
pkg/extensions/extension-config-disabled.go	100.00% <100.00%> (ø)
... and 7 more

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