chore(rules): Add metrics on Redis operations

[ceorourke]

Add Datadog metrics when we perform a Redis operation.

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 77.91%. Comparing base (b0d328d) to head (235ef69). Report is 12 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #71143      +/-   ##
==========================================
- Coverage   77.91%   77.91%   -0.01%     
==========================================
  Files        6525     6526       +1     
  Lines      290661   290663       +2     
  Branches    50294    50294              
==========================================
- Hits       226466   226463       -3     
- Misses      57947    57951       +4     
- Partials     6248     6249       +1     

Files	Coverage Δ
src/sentry/buffer/redis.py	88.23% <100.00%> (+0.07%)	:arrow_up:

... and 29 files with indirect coverage changes