ref(metrics): move metrics samples endpoint to own file

[shellmayr]

Contributes to https://github.com/getsentry/sentry/issues/71228

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 96.72131% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 77.85%. Comparing base (f535fed) to head (436ed16). Report is 4 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #71319      +/-   ##
==========================================
- Coverage   77.85%   77.85%   -0.01%     
==========================================
  Files        6533     6534       +1     
  Lines      291110   291139      +29     
  Branches    50377    50379       +2     
==========================================
+ Hits       226657   226679      +22     
- Misses      58218    58227       +9     
+ Partials     6235     6233       -2     

Files	Coverage Δ
src/sentry/api/endpoints/organization_metrics.py	87.40% <100.00%> (-1.27%)	:arrow_down:
src/sentry/api/urls.py	100.00% <100.00%> (ø)
...ntry/api/endpoints/organization_metrics_samples.py	96.49% <96.49%> (ø)

... and 15 files with indirect coverage changes