🔧 chore: GA slack multi team linking

[iamrajjoshi]

Slack multi team single channel linking has been GA'ed for a while and i was able to track down the bug in the sentry workspace to something unrelated so cleaning up the code now. will have a follow up pr in options, then a final one here to remove the handler.

I need to do it this way cause customers will have a disruption when trying to link/unlink if i don't set the default first.

oh also, we can remove an slo reason with this feature add.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #82746      +/-   ##
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+ Coverage   87.39%   87.49%   +0.10%     
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  Files        9409     9409              
  Lines      538560   538530      -30     
  Branches    21037    21034       -3     
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+ Hits       470691   471212     +521     
+ Misses      67498    66947     -551     
  Partials      371      371