feat(trace): Add timeouts to the trace query

[wmak]

• This adds a timeout to the queries for the trace endpoint so that the entire endpoint doesn't fail if one of the datasets takes too long to execute
• Had to switch to multiprocessing because ThreadPoolExecutor doesn't have a good way to kill running tasks when they hit timeout? afaict it will wait until all tasks finish before letting you do anything

[codecov[bot]]

Codecov Report

:x: Patch coverage is 89.47368% with 2 lines in your changes missing coverage. Please review. :white_check_mark: All tests successful. No failed tests found.

Files with missing lines	Patch %	Lines
src/sentry/snuba/trace.py	88.88%	2 Missing :warning:

Additional details and impacted files

@@             Coverage Diff              @@
##           master   #104554       +/-   ##
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+ Coverage   65.78%    80.54%   +14.76%     
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  Files        9338      9346        +8     
  Lines      399925    400312      +387     
  Branches    25621     25621               
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+ Hits       263087    322429    +59342     
+ Misses     136389     77434    -58955     
  Partials      449       449