Setup Tigris test cases with explicit schemas

[rumyantseva]

Description

Refs #906. As we support JSON Schema validators for Tigris, in tests let's create collections by defining them explicitly.
This PR is preparation for #1005.

Readiness checklist

• I added tests for new functionality or bugfixes.
• I ran task all, and it passed.
• I added/updated comments for both exported and unexported top-level declarations (functions, types, etc).
• I checked comments rendering with task godocs.
• I ensured that the title is good enough for the changelog.
• (for maintainers only) I set Reviewers (@FerretDB/core), Assignee, Labels, Project and project's Sprint fields.
• I marked all done items in this checklist.

[vercel]

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Name	Status	Preview	Updated
ferret-db	✅ Ready (Inspect)	Visit Preview	Sep 28, 2022 at 8:30AM (UTC)

[codecov]

Codecov Report

Merging #1167 (b31497e) into main (c2fba8e) will decrease coverage by 0.05%.
The diff coverage is 100.00%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1167      +/-   ##
==========================================
- Coverage   66.38%   66.33%   -0.06%     
==========================================
  Files         250      251       +1     
  Lines       12256    12293      +37     
==========================================
+ Hits         8136     8154      +18     
- Misses       3232     3248      +16     
- Partials      888      891       +3     

Impacted Files	Coverage Δ
integration/setup/setup.go	87.25% <100.00%> (+0.79%)	⬆️
integration/setup/setup_compat.go	88.39% <100.00%> (+0.77%)	⬆️
integration/shareddata/scalars.go	100.00% <100.00%> (ø)
integration/shareddata/shareddata.go	85.33% <100.00%> (+2.25%)	⬆️
internal/tjson/schema.go	77.62% <100.00%> (+0.64%)	⬆️
internal/util/version/version.go	55.00% <0.00%> (-5.00%)	⬇️
internal/handlers/pg/pgdb/settings.go	39.53% <0.00%> (-4.66%)	⬇️
internal/handlers/pg/pgdb/query.go	40.68% <0.00%> (-2.76%)	⬇️
internal/handlers/common/filter.go	86.58% <0.00%> (-0.95%)	⬇️
internal/handlers/tigris/json_schema.go	100.00% <0.00%> (+15.78%)	⬆️

Flag	Coverage Δ
integration	62.62% <100.00%> (-0.01%)	⬇️
mongodb	14.89% <37.83%> (+0.04%)	⬆️
pg	51.86% <40.54%> (-0.19%)	⬇️
tigris	34.67% <94.59%> (+0.18%)	⬆️
unit	24.00% <25.00%> (-0.06%)	⬇️

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

[noisersup]

Overall LGTM,
I pointed one more place where we should declare the variable in place of initialization

[w84thesun]

LGTM

[AlekSi]

LGTM