ref(querybuilder): Clean up the way we load configs

[wmak]

• Instead of a giant if statement for every dataset in the base query builder, set the config in a load config function in each builder

[getsantry]

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 🥀

[codecov]

Codecov Report

Attention: Patch coverage is 95.55556% with 2 lines in your changes missing coverage. Please review.

Project coverage is 78.00%. Comparing base (486a589) to head (ab28d60).
Report is 54 commits behind head on master.

❗ Current head ab28d60 differs from pull request most recent head 823c6bc

Please upload reports for the commit 823c6bc to get more accurate results.

Additional details and impacted files

@@            Coverage Diff             @@
##           master   #71710      +/-   ##
==========================================
- Coverage   78.01%   78.00%   -0.01%     
==========================================
  Files        6630     6632       +2     
  Lines      295916   296055     +139     
  Branches    50971    50988      +17     
==========================================
+ Hits       230848   230938      +90     
- Misses      58732    58780      +48     
- Partials     6336     6337       +1     

Files	Coverage Δ
src/sentry/search/events/builder/metrics.py	88.51% <100.00%> (+0.16%)	⬆️
.../sentry/search/events/builder/metrics_summaries.py	85.71% <100.00%> (+2.38%)	⬆️
.../sentry/search/events/builder/profile_functions.py	89.88% <100.00%> (+0.35%)	⬆️
...search/events/builder/profile_functions_metrics.py	83.33% <100.00%> (+1.51%)	⬆️
src/sentry/search/events/builder/sessions.py	87.09% <100.00%> (+0.88%)	⬆️
src/sentry/search/events/builder/spans_indexed.py	100.00% <100.00%> (ø)
src/sentry/search/events/builder/spans_metrics.py	100.00% <100.00%> (ø)
src/sentry/snuba/metrics/query_builder.py	90.35% <100.00%> (+0.03%)	⬆️
src/sentry/search/events/builder/discover.py	92.60% <88.88%> (-0.34%)	⬇️

... and 59 files with indirect coverage changes