fix: DEV-1920: Review performance and other speed ups

[makseq]

No description provided.

[codecov]

Codecov Report

Merging #2158 (3022e09) into master (a757398) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master    #2158   +/-   ##
=======================================
  Coverage   78.05%   78.05%           
=======================================
  Files         137      137           
  Lines        9903     9903           
=======================================
  Hits         7730     7730           
  Misses       2173     2173           

Impacted Files	Coverage Δ
label_studio/label_studio/tasks/models.py	90.05% <0.00%> (ø)
label_studio/label_studio/webhooks/models.py	96.66% <0.00%> (ø)

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[triklozoid]

I think it's better to create indexes only for fields, where we really need them.