Add Elasticsearch 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 #337 (f745604) into rework-kobs-architecture (a32a80d) will increase coverage by 1.15%.
The diff coverage is 100.00%.

@@                     Coverage Diff                      @@
##           rework-kobs-architecture     #337      +/-   ##
============================================================
+ Coverage                     45.95%   47.10%   +1.15%     
============================================================
  Files                            94       96       +2     
  Lines                          6472     6613     +141     
============================================================
+ Hits                           2974     3115     +141     
  Misses                         3433     3433              
  Partials                         65       65              

Impacted Files	Coverage Δ
plugins/plugin-grafana/pkg/instance/instance.go	100.00% <ø> (ø)
plugins/plugin-elasticsearch/cmd/elasticsearch.go	100.00% <100.00%> (ø)
...gins/plugin-elasticsearch/pkg/instance/instance.go	100.00% <100.00%> (ø)

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