feat(uptime): Make consumer able to run in parallel

[wedamija]

This adds thread pool parallelization to the uptime consumer. We should potentially consider process parallelizatoin as well, so that we can take advantage of all cores.

This is a rough draft of this and isn't tested - based off the issue occurrence consumer and monitor consumer.

[codecov]

Codecov Report

Attention: Patch coverage is 53.84615% with 30 lines in your changes missing coverage. Please review.

✅ All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
.../remote_subscriptions/consumers/result_consumer.py	53.22%	29 Missing ⚠️
src/sentry/uptime/consumers/results_consumer.py	66.66%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #81409      +/-   ##
==========================================
- Coverage   80.38%   80.37%   -0.01%     
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  Files        7231     7231              
  Lines      319909   319968      +59     
  Branches    20806    20806              
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+ Hits       257145   257173      +28     
- Misses      62374    62405      +31     
  Partials      390      390