feat(discover): Adds cache_miss_rate function to discover metrics dataset

[edwardgou-sentry]

Adds the cache_miss_rate function to the discover metrics dataset

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 88.88889% with 1 line in your changes missing coverage. Please review.

:white_check_mark: All tests successful. No failed tests found.

Files	Patch %	Lines
src/sentry/search/events/datasets/metrics.py	88.88%	1 Missing :warning:

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #75896       +/-   ##
===========================================
- Coverage   90.49%   78.27%   -12.23%     
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  Files        3099     6824     +3725     
  Lines      193934   303955   +110021     
  Branches        0    52289    +52289     
===========================================
+ Hits       175504   237923    +62419     
- Misses      18430    59644    +41214     
- Partials        0     6388     +6388     

[edwardgou-sentry]

There's some duplicate resolve functions between this metrics dataset and the spans_metrics dataset. Planning to look into consolidating these in a later pr