Add review checklist to new PRs

[sloede]

As discussed on Slack and in #1607.

Resolves #1529, closes #1607.

Needs trixi-framework/add-pr-review-checklist#2 to be merged first and v1 to be tagged there. EDIT: done

[codecov]

Codecov Report

Merging #1609 (d9517bf) into main (add3a7f) will decrease coverage by 7.61%.
Report is 1 commits behind head on main.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #1609      +/-   ##
==========================================
- Coverage   91.12%   83.51%   -7.61%     
==========================================
  Files         414      414              
  Lines       33929    33922       -7     
==========================================
- Hits        30917    28329    -2588     
- Misses       3012     5593    +2581     

Flag	Coverage Δ
unittests	83.51% <ø> (-7.61%)	⬇️

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see 117 files with indirect coverage changes

[jlchan]

Thanks! LGTM