Add blog post on "How to run FerretDB on top of StackGres"

[Fashander]

Description

Readiness checklist

• I added/updated unit tests.
• I added/updated integration/compatibility tests.
• 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), Labels, Project and project's Sprint fields.
• I marked all done items in this checklist.

[mergify]

Marketing blog posts should be reviewed by @ptrfarkas and @AlekSi.

[codecov]

Codecov Report

Merging #2869 (a34b1f3) into main (8e2abca) will decrease coverage by 4.11%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #2869      +/-   ##
==========================================
- Coverage   76.50%   72.39%   -4.11%     
==========================================
  Files         386      386              
  Lines       21120    21120              
==========================================
- Hits        16158    15290     -868     
- Misses       4044     4901     +857     
- Partials      918      929      +11     

see 37 files with indirect coverage changes

Flag	Coverage Δ
hana	?
integration	68.76% <ø> (-4.26%)	⬇️
mongodb	5.41% <ø> (ø)
pg	58.01% <ø> (-8.32%)	⬇️
shard-1	54.24% <ø> (-0.04%)	⬇️
shard-2	55.76% <ø> (+0.01%)	⬆️
shard-3	37.32% <ø> (-19.87%)	⬇️
sqlite	46.53% <ø> (-0.09%)	⬇️
unit	24.23% <ø> (-0.03%)	⬇️

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