[app] Delete all cookies on signout

[ricoberger]

Until now we only deleted the main cookie when the user clicks the
signout button. This is now changed so that all cookies are deleted.
This means that also the cookies generated by plugins are deleted when
they are starting with "kobs".

• 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 #421 (fba9a98) into main (3a1e4ed) will increase coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##             main     #421      +/-   ##
==========================================
+ Coverage   45.60%   45.61%   +0.01%     
==========================================
  Files         139      139              
  Lines       11888    11892       +4     
==========================================
+ Hits         5421     5425       +4     
  Misses       6328     6328              
  Partials      139      139              

Impacted Files	Coverage Δ
pkg/hub/auth/auth.go	72.58% <100.00%> (+0.43%)	⬆️

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