Use tox and pre-commit for testing

[roaldnefs]

Use tox and pre-commit for testing to allow users to locally test by only having to install those two dependencies.

This commit also simplifies and merges the GitHub workflows build and lint, as they are now two steps in the tox worflow.

[jbouter]

Brilliant work! Thanks. Should we start including documentation specifically on how to contribute and set up a dev environment for salt-lint? I feel there's a growing amount of specifics. I reckon pre-commit hooks aren't going to magically work on their own.

[roaldnefs]

Brilliant work! Thanks. Should we start including documentation specifically on how to contribute and set up a dev environment for salt-lint? I feel there's a growing amount of specifics. I reckon pre-commit hooks aren't going to magically work on their own.

I suppose we should indeed start to write some documentation about how to contribute to salt-lint. I'm thinking about adding a docs directory and using Sphinx to automatically generated the documentation. This would allow the removal/deprecation of the GitHub wiki, thus making it possible to include any required documentation in a pull request instead of having to manually add it after the pull request has been merged.