Replace requirement files with pyproject

[dafeda]

Pre review checklist

• Read through the code changes carefully after finishing work
• Make sure tests pass locally (after every commit!)
• Prepare changes in small commits for more convenient review (optional)
• PR title captures the intent of the changes, and is fitting for release notes.
• Updated documentation
• Ensured that unit tests are added for all new behavior (See
  Ground Rules),
  and changes to existing code have good test coverage.

Pre merge checklist

• Added appropriate release note label
• Commit history is consistent and clean, in line with the contribution guidelines.

[codecov-commenter]

Codecov Report

Merging #6116 (46214a7) into main (1017487) will increase coverage by 0.01%.
Report is 1 commits behind head on main.
The diff coverage is n/a.

@@            Coverage Diff             @@
##             main    #6116      +/-   ##
==========================================
+ Coverage   82.45%   82.46%   +0.01%     
==========================================
  Files         350      350              
  Lines       21423    21423              
  Branches      839      839              
==========================================
+ Hits        17664    17667       +3     
+ Misses       3461     3458       -3     
  Partials      298      298              

Files Changed	Coverage Δ
src/ert/dark_storage/endpoints/responses.py	100.00% <ø> (ø)

... and 2 files with indirect coverage changes

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[berland]

this line was removed further up, it should not be removed here?

[frode-aarstad]

LGTM