Improve how we select index forcing for CRDB

[josephschorr]

This uses a less hand-written method and more structural and well tested method to select which index to force, if any

[codecov]

Codecov Report

Attention: Patch coverage is 85.24590% with 27 lines in your changes missing coverage. Please review.

Project coverage is 77.40%. Comparing base (328a634) to head (f71fdcc).

Files with missing lines	Patch %	Lines
internal/datastore/crdb/schema/indexutil.go	88.47%	13 Missing and 5 partials ⚠️
internal/datastore/crdb/reader.go	25.00%	2 Missing and 1 partial ⚠️
internal/datastore/crdb/readwrite.go	40.00%	2 Missing and 1 partial ⚠️
internal/datastore/crdb/schema/forcedindex.go	75.00%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2458      +/-   ##
==========================================
+ Coverage   77.39%   77.40%   +0.01%     
==========================================
  Files         422      424       +2     
  Lines       51275    51391     +116     
==========================================
+ Hits        39679    39773      +94     
- Misses       9094     9110      +16     
- Partials     2502     2508       +6     

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