Add Harbor plugin

[ricoberger]

• I added a CHANGELOG entry for this change.
• I adjusted the corresponding documentation for this change.
• I adjusted the values.yaml file and the documentation for all values.

[codecov-commenter]

Codecov Report

Merging #335 (d77aff1) into rework-kobs-architecture (7cd6ad1) will decrease coverage by 1.03%.
The diff coverage is 28.87%.

@@                     Coverage Diff                      @@
##           rework-kobs-architecture     #335      +/-   ##
============================================================
- Coverage                     49.46%   48.43%   -1.04%     
============================================================
  Files                            86       89       +3     
  Lines                          5359     5643     +284     
============================================================
+ Hits                           2651     2733      +82     
- Misses                         2647     2847     +200     
- Partials                         61       63       +2     

Impacted Files	Coverage Δ
plugins/plugin-harbor/pkg/instance/instance.go	16.85% <16.85%> (ø)
plugins/plugin-harbor/cmd/harbor.go	19.49% <19.49%> (ø)
plugins/plugin-harbor/pkg/instance/request.go	100.00% <100.00%> (ø)

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