[app] Add Integrations for Kubernetes Resources

[ricoberger]

Add a new integrations feature for kobs. In this first iteration we
implemented the suggested integrations feature from #255 for Kubernetes
Resources.

This integration allows an administrator of kobs to add a set of default
dashboards to Kubernetes Resources. This way we can add for example a
resource usage dashboard to all Pods, without that each Pod must have
the "kobs.io/dashboards" annotation.

The configured dashboards in the integrations and the dashboards from
the "kobs.io/dashboards" annotation are always merged and not
overwritte.

• 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 #401 (13b86b8) into main (4490c9f) will decrease coverage by 0.04%.
The diff coverage is 16.66%.

@@            Coverage Diff             @@
##             main     #401      +/-   ##
==========================================
- Coverage   45.70%   45.66%   -0.05%     
==========================================
  Files         137      137              
  Lines       10661    10672      +11     
==========================================
  Hits         4873     4873              
- Misses       5695     5706      +11     
  Partials       93       93              

Impacted Files	Coverage Δ
pkg/hub/api/plugins/plugins.go	0.00% <0.00%> (ø)
pkg/hub/api/resources/resources.go	0.00% <0.00%> (ø)
pkg/hub/hub.go	0.00% <0.00%> (ø)
pkg/hub/api/applications/applications.go	100.00% <100.00%> (ø)
pkg/hub/api/clusters/clusters.go	100.00% <100.00%> (ø)
pkg/hub/api/dashboards/dashboards.go	100.00% <100.00%> (ø)
pkg/hub/api/teams/teams.go	100.00% <100.00%> (ø)

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