Run entities-service validate as a pre-commit hook

[CasperWA]

Closes #122

Add a pre-commit hook with id validate-entities.
It runs on all known file formats as well as with --verbose.

One can add extra options through the pre-commit args.
Finally, in its current version, one must add ``.[cli]'to the pre-commitadditional_dependencies`.

A separate test job has been set up to test the hook.

---

Important

NB: This will deprecate the --file/-f and --dir/-d options from the validate and update commands in favor of a SOURCE argument, which may be given multiple times.

---

Note: The commits have been squashed down to two commits, each representing the introduction of SOURCE (and deprecation of --file/-f and --dir/-d) and the new pre-commit hooks validate-entities, respectively.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.11%. Comparing base (7b8c796) to head (49b9f0b).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #126      +/-   ##
==========================================
+ Coverage   92.04%   92.11%   +0.07%     
==========================================
  Files          26       26              
  Lines        1320     1332      +12     
==========================================
+ Hits         1215     1227      +12     
  Misses        105      105              

Flag	Coverage Δ
docker	80.03% <100.00%> (+0.18%)	⬆️
local	90.99% <100.00%> (+0.08%)	⬆️

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[CasperWA]

The two commits 7bd888a and 1ced968 were what made up this PR.
Due to an extra merge commit in this PR branch' HEAD, GitHub could not recognize that this PR has been merged into main. Instead, when rebasing these commits onto main, it was found locally that this would result in a noop (indeed ...), and after pushing that, the PR has been closed.

TL;DR: This PR was successfully merged (not closed), adding the commits 7bd888a and 1ced968 to main.