feat(metrics): MRI support for metrics API

[obostjancic]

Part of: https://github.com/getsentry/getsentry/issues/10656

Enables usage of MRI as an identifier when querying the metrics API.

Notable changes:

• OrganizationMetricsEndpoint (metrics/meta) is redesigned and returns all available metrics.
• OrganizationMetricsDataEndpoint (metrics/data) now supports passing MRIs in field query param. For example field=sum(c:sessions/all@none) is valid and equivalent to field=sum(session.all)

[codecov]

Codecov Report

Merging #50404 (e551e95) into master (268804e) will decrease coverage by 0.01%.
The diff coverage is 90.90%.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #50404      +/-   ##
==========================================
- Coverage   81.16%   81.16%   -0.01%     
==========================================
  Files        4861     4861              
  Lines      203823   203827       +4     
  Branches    11159    11159              
==========================================
+ Hits       165435   165438       +3     
- Misses      38142    38143       +1     
  Partials      246      246              

Impacted Files	Coverage Δ
src/sentry/snuba/metrics/naming_layer/mapping.py	94.73% <80.00%> (-1.49%)	⬇️
src/sentry/snuba/metrics/query_builder.py	93.26% <86.95%> (-0.45%)	⬇️
src/sentry/api/endpoints/organization_metrics.py	97.82% <100.00%> (+0.91%)	⬆️
src/sentry/snuba/metrics/datasource.py	98.34% <100.00%> (+0.91%)	⬆️

... and 3 files with indirect coverage changes

[iambriccardo]

Great work, left some minor comments!

[iambriccardo]

🚢