Add blog post for FerretDB v1.6.0

[Fashander]

Description

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), 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 #3058 (12665d7) into main (2b469b4) will decrease coverage by 0.04%.
The diff coverage is n/a.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #3058      +/-   ##
==========================================
- Coverage   76.44%   76.41%   -0.04%     
==========================================
  Files         386      386              
  Lines       21154    21154              
==========================================
- Hits        16172    16164       -8     
- Misses       4055     4061       +6     
- Partials      927      929       +2     

see 8 files with indirect coverage changes

Flag	Coverage Δ
hana	?
integration	72.93% <ø> (-0.04%)	⬇️
mongodb	5.54% <ø> (ø)
pg	66.31% <ø> (+0.02%)	⬆️
shard-1	54.75% <ø> (ø)
shard-2	54.96% <ø> (-0.12%)	⬇️
shard-3	57.65% <ø> (-0.03%)	⬇️
sqlite	46.70% <ø> (-0.07%)	⬇️
unit	24.21% <ø> (+0.02%)	⬆️

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