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]

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

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