Make batch sizes configurable

[kropidlowsky]

Description

Replaced batch sizes hard-cored values with configuratable for: sqlite, postgrsql, hana.

Closes #3708.

Readiness checklist

• I added/updated unit tests (and they pass).
• I added/updated integration/compatibility tests (and they pass).
• I added/updated comments and checked rendering.
• I made spot refactorings.
• I updated user documentation.
• I ran task all, and it passed.
• I ensured that PR title is good enough for the changelog.
• (for maintainers only) I set Reviewers (@FerretDB/core), Milestone (Next), Labels, Project and project's Sprint fields.
• I marked all done items in this checklist.

[codecov]

Codecov Report

Attention: Patch coverage is 71.05263% with 11 lines in your changes are missing coverage. Please review.

Project coverage is 73.90%. Comparing base (aea56ea) to head (0a86ac7).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4149      +/-   ##
==========================================
- Coverage   74.61%   73.90%   -0.72%     
==========================================
  Files         339      339              
  Lines       22862    22876      +14     
==========================================
- Hits        17059    16906     -153     
- Misses       4498     4684     +186     
+ Partials     1305     1286      -19     

Files	Coverage Δ
integration/setup/listener.go	70.94% <100.00%> (-3.89%)	⬇️
integration/setup/setup.go	84.74% <ø> (ø)
internal/backends/postgresql/backend.go	71.42% <100.00%> (ø)
internal/backends/postgresql/metadata/registry.go	71.54% <100.00%> (+0.05%)	⬆️
internal/backends/sqlite/backend.go	80.39% <100.00%> (ø)
internal/backends/sqlite/metadata/registry.go	70.58% <100.00%> (+0.10%)	⬆️
internal/handler/handler.go	50.86% <ø> (ø)
internal/handler/msg_insert.go	82.69% <100.00%> (-0.17%)	⬇️
internal/handler/registry/postgresql.go	85.18% <100.00%> (+1.18%)	⬆️
internal/handler/registry/registry.go	44.44% <ø> (ø)
... and 7 more

... and 11 files with indirect coverage changes

Flag	Coverage Δ
filter-true	67.38% <71.05%> (-0.81%)	⬇️
hana-1	?
integration	67.38% <71.05%> (-0.81%)	⬇️
mongodb-1	5.13% <0.00%> (-0.02%)	⬇️
postgresql-1	46.48% <39.47%> (+0.03%)	⬆️
postgresql-2	49.56% <39.47%> (-0.10%)	⬇️
postgresql-3	49.84% <39.47%> (+0.02%)	⬆️
sqlite-1	45.68% <42.10%> (+0.03%)	⬆️
sqlite-2	48.78% <42.10%> (+0.04%)	⬆️
sqlite-3	49.00% <42.10%> (-0.02%)	⬇️
unit	32.51% <48.64%> (-0.01%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

[AlekSi]

Tests fail because we don't pass BatchSize somewhere, and invalid SQL is generated for INSERT

[chilagrow]

Thanks for your contribution!

[rumyantseva]

Thanks for contributing!

[AlekSi]

Thank you!