[app] Add recover handler for metrics middleware

[ricoberger]

We now have a recover handler for the "httpmetrics" middleware. We also
renamed the metrics to "kobs_requests_total",
"kobs_request_duration_seconds" and "kobs_request_size_bytes".

• 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 #400 (8a6e8b4) into main (03b01a9) will decrease coverage by 0.02%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##             main     #400      +/-   ##
==========================================
- Coverage   45.87%   45.84%   -0.03%     
==========================================
  Files         137      137              
  Lines       10634    10640       +6     
==========================================
  Hits         4878     4878              
- Misses       5671     5677       +6     
  Partials       85       85              

Impacted Files	Coverage Δ
pkg/middleware/httpmetrics/httpmetrics.go	0.00% <0.00%> (ø)

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