Ignore $readPreferences for insert

[AlekSi]

Description

The latest mongosh sends it:

rs0 [direct: primary] test> db.lala.insertOne({})
MongoServerError[FailedToParse]: insert: unknown field "$readPreference"

See also #3996.

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

All modified and coverable lines are covered by tests ✅

Project coverage is 74.02%. Comparing base (b8d1f60) to head (e1985a4).

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4440      +/-   ##
==========================================
+ Coverage   73.96%   74.02%   +0.06%     
==========================================
  Files         327      327              
  Lines       22674    22674              
==========================================
+ Hits        16770    16785      +15     
+ Misses       4672     4663       -9     
+ Partials     1232     1226       -6     

Files	Coverage Δ
internal/handler/common/insert.go	100.00% <ø> (ø)

... and 6 files with indirect coverage changes

Flag	Coverage Δ
filter-true	66.89% <ø> (+0.06%)	⬆️
hana-1	?
integration	66.89% <ø> (+0.06%)	⬆️
mongodb-1	5.30% <ø> (ø)
postgresql-1	42.38% <ø> (-0.02%)	⬇️
postgresql-2	42.35% <ø> (+0.04%)	⬆️
postgresql-3	42.12% <ø> (ø)
postgresql-4	43.69% <ø> (-0.01%)	⬇️
postgresql-5	45.11% <ø> (+0.02%)	⬆️
sqlite-1	41.55% <ø> (+<0.01%)	⬆️
sqlite-2	41.60% <ø> (-0.01%)	⬇️
sqlite-3	41.35% <ø> (-0.02%)	⬇️
sqlite-4	42.84% <ø> (-0.03%)	⬇️
sqlite-5	44.35% <ø> (+0.01%)	⬆️
unit	33.72% <ø> (ø)

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