RFC: ocamlformat reloaded

Redoing !1131 (closed) with ocmalformat.0.10, and putting the changes in ≠ commits:

• Actual manual changes:
  • Add script to update .ocamlformat files
  • Update lint.sh for ocamlformat
  • Replace make fix-lint with make fmt
  • Rename get-git-info.ml → get-git-info.mlt
• semi-automatic changes:
  • Update .ocamlformat files
  • Run make fmt #WhiteSpace
• Quick hack of the CI to try the whole pipeline:
  • Add temporary CI fix (install ocamlformat) #WIP

This CI-job: jobs/260407765 is an example of job that failed because of the lint check (I had modified get-git-info.mlt).

Still to do, if we go with this:

• Remove all the @runtest_lint from the dune files or just fix them for good (I think they at least need all to depend on the .ocamlformat file so that it shows up in the _build/ directory).
• Document somewhere what the scripts do.
• Add ocamlformat to the opam-repository and remove ocp-indent, then update the .gitlab-ci.yml.