chore(similarity): Add killswitches for each feature flag

[jangjodi]

Add killswitches for each feature flag since these are now managed in feature handlers in getsentry
We will check the killswitch in the feature handler so we can turn off the feature faster

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 78.11%. Comparing base (43b5124) to head (5fb39bf).
Report is 5 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #74274      +/-   ##
==========================================
- Coverage   78.11%   78.11%   -0.01%     
==========================================
  Files        6665     6665              
  Lines      298007   298011       +4     
  Branches    51291    51291              
==========================================
+ Hits       232776   232779       +3     
- Misses      58955    58957       +2     
+ Partials     6276     6275       -1     

Files	Coverage Δ
src/sentry/options/defaults.py	100.00% <100.00%> (ø)

... and 3 files with indirect coverage changes