Newrelic add metrics

[lojzatran]

I added the custom metrics. The metric naming is according to the rules from NewRelic: https://docs.newrelic.com/docs/apm/agents/manage-apm-agents/agent-data/collect-custom-metrics/.

I picked metric timesliced data: https://docs.newrelic.com/docs/data-apis/understand-data/new-relic-data-types/#metrics-new-relic. It is 4x faster than using Metric API as it uses APM to submit metrics. On the other hand it does not support dimensions and the other suggested workarounds are not ideal (https://stackoverflow.com/questions/68366017/recording-custom-dimensional-metrics-in-new-relic).

I also updated the docs: https://github.com/commercetools/commercetools-docs/pull/4963

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 30 lines in your changes are missing coverage. Please review.

Project coverage is 10.68%. Comparing base (29dd4b3) to head (5fd5de3).
Report is 31 commits behind head on main.

Files	Patch %	Lines
...onitoring/newrelic/NewrelicResponseSerializer.java	0.00%	23 Missing ⚠️
...nitoring/newrelic/NewRelicTelemetryMiddleware.java	0.00%	6 Missing ⚠️
...ommercetools/monitoring/newrelic/NewrelicInfo.java	0.00%	1 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff              @@
##               main     #630      +/-   ##
============================================
+ Coverage     10.60%   10.68%   +0.07%     
- Complexity     1842     1853      +11     
============================================
  Files          6220     6230      +10     
  Lines         59405    59572     +167     
  Branches        265      270       +5     
============================================
+ Hits           6299     6364      +65     
- Misses        52941    53043     +102     
  Partials        165      165              

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[jenschude]

Small change only