Add Tembo QA blog post

[Fashander]

Description

Closes FerretDB/engineering#155.

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.

[mergify]

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

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (6893544) 76.05% compared to head (463029f) 74.87%.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #4081      +/-   ##
==========================================
- Coverage   76.05%   74.87%   -1.18%     
==========================================
  Files         347      347              
  Lines       22168    22168              
==========================================
- Hits        16860    16599     -261     
- Misses       3988     4294     +306     
+ Partials     1320     1275      -45     

see 20 files with indirect coverage changes

Flag	Coverage Δ
filter-true	66.41% <ø> (-1.39%)	⬇️
hana-1	?
integration	66.41% <ø> (-1.39%)	⬇️
mongodb-1	4.73% <ø> (ø)
postgresql-1	48.16% <ø> (?)
postgresql-2	47.73% <ø> (+<0.01%)	⬆️
postgresql-3	47.87% <ø> (ø)
sqlite-1	47.36% <ø> (+0.04%)	⬆️
sqlite-2	46.90% <ø> (-0.05%)	⬇️
sqlite-3	47.04% <ø> (ø)
unit	32.94% <ø> (ø)

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