feat(issue-search): Remove `groups.enable-post-update-signal`

[snigdhas]

Remove references to groups.enable-post-update-signal and enable the option globally. This allows us to stop sending custom post-update signals since the call to .update will send the signal inherently.

The option configurations will be removed in followup PR after which the option can be unregistered.

[codecov[bot]]

Codecov Report

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

Project coverage is 77.63%. Comparing base (b403ecc) to head (7b76356). Report is 1056 commits behind head on master.

Additional details and impacted files

@@             Coverage Diff             @@
##           master   #74607       +/-   ##
===========================================
+ Coverage   56.96%   77.63%   +20.67%     
===========================================
  Files        6459     6690      +231     
  Lines      285436   299465    +14029     
  Branches    49078    51529     +2451     
===========================================
+ Hits       162597   232504    +69907     
+ Misses     118412    60653    -57759     
- Partials     4427     6308     +1881     

Files	Coverage Δ
src/sentry/api/helpers/group_index/update.py	90.17% <100.00%> (+47.48%)	:arrow_up:
src/sentry/db/models/manager/base_query_set.py	84.90% <100.00%> (+39.74%)	:arrow_up:
src/sentry/db/models/query.py	67.25% <100.00%> (+9.99%)	:arrow_up:
src/sentry/issues/escalating.py	91.03% <100.00%> (+35.78%)	:arrow_up:
src/sentry/issues/ongoing.py	100.00% <ø> (+58.62%)	:arrow_up:
src/sentry/issues/status_change.py	93.75% <ø> (+20.67%)	:arrow_up:
src/sentry/models/activity.py	93.81% <ø> (+17.62%)	:arrow_up:
src/sentry/models/group.py	94.87% <100.00%> (+37.89%)	:arrow_up:
src/sentry/options/defaults.py	100.00% <ø> (ø)

... and 2089 files with indirect coverage changes

[getsantry[bot]]

This pull request has gone three weeks without activity. In another week, I will close it.

But! If you comment or otherwise update it, I will reset the clock, and if you add the label WIP, I will leave it alone unless WIP is removed ... forever!

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"A weed is but an unloved flower." ― Ella Wheeler Wilcox 🥀