[app] Fix tooltip in charts

[ricoberger]

This is another fix for the tooltip handling in the charts. This is
required, because sometimes it could happen that we get an error when we
tried to render the tooltip.

• 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 #387 (b2ca68b) into main (b9604c8) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##             main     #387   +/-   ##
=======================================
  Coverage   45.26%   45.26%           
=======================================
  Files         132      132           
  Lines       10314    10314           
=======================================
  Hits         4669     4669           
  Misses       5567     5567           
  Partials       78       78           

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