ref(ddm): Rename the files for metrics metadata

[iambriccardo]

This PR renames all the files for metrics metadata with the metrics_* prefix to make them faster to recognize and disambiguate.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (cbb5661) 81.39% compared to head (8730520) 81.39%.
Report is 3 commits behind head on master.

❗ Current head 8730520 differs from pull request most recent head 1c26bcf. Consider uploading reports for the commit 1c26bcf to get more accurate results

Additional details and impacted files

@@           Coverage Diff           @@
##           master   #63931   +/-   ##
=======================================
  Coverage   81.39%   81.39%           
=======================================
  Files        5227     5227           
  Lines      232447   232447           
  Branches    40248    40248           
=======================================
  Hits       189205   189205           
- Misses      37390    37393    +3     
+ Partials     5852     5849    -3     

Files	Coverage Δ
src/sentry/api/endpoints/organization_ddm.py	94.73% <100.00%> (ø)
...y/api/serializers/models/metrics_code_locations.py	100.00% <100.00%> (ø)
...try/api/serializers/models/metrics_correlations.py	100.00% <100.00%> (ø)
...etrics/querying/metadata/metrics_code_locations.py	93.00% <ø> (ø)
..._metrics/querying/metadata/metrics_correlations.py	81.81% <ø> (ø)

... and 7 files with indirect coverage changes