Add CI checks

[jlesquembre]

In my last PR, a small issue went unnoticed. I fixed it, and added some CI checks.

For now, only the frontend part is checked, we can add more checks in another PR.

Some additional changes I did, which are open to discussion:

• Add check/format-nix commands, but replaced nixfmt with nixpkgs-fmt. I personally don't prefer one over the other, but the CLI interface for nixpkgs-fmt is nicer. You can check/format all nix files at once. nixfmt doesn't offer a bulk option.
• Replaced poetry run black/isort ... with black/isort .... Those binaries are provided by nixpkgs, that way we can skip the poetry install ... command, and auto-format the etl sub-project too

[jlesquembre]

@dorranh makes sense, I didn't think the issue you mentioned. I'm reverting the python related changes. I agree with you about poetry2nix, but better to do those changes in a different PR

[GuillaumeDesforges]

Ideally we would want to run checks in the folder of each packages.

Maybe something like this could be done?

find . -name 'pyproject.toml' | xargs dirname | xargs -{} sh -c 'cd {} && black . && flake8 .'

[jlesquembre]

@GuillaumeDesforges That could be an option too. I probably tried to do too much on this PR, I'm reverting the python changes to focus only on the frontend part (which doesn't work on current main)