CI: add a linting step for all of our custom bitbake recipes

[hnez]

This PR is inspired by #110, which mentions running meta-openembedded's oe-stylize.py on the bitbakes files in meta-lxatac.

Now that I have learned that there is a linter script for bitbake files I want it as a GitHub action.

So here is a pull request to add it.

TODO before merging:

• Make sure the action runs without errors

[ejoerns]

@hnez While I like the idea in general, I have some objections against running this in CI: The script is not too actively maintained (primarily got some PEP8-related fixes over the last years) and is not part of oe-core. I have seen several false positives I had to re-fix manually in some recipes (like when properly using self-defined variables).

Thus I'd say it is a good tool for running manually on your recipe, but I am not sure if we should enforce it in CI automatically.

[hnez]

I've just rebased the PR, just to have a second look at the output of the job.

On the one hand I really like having one canonical version of source files with their formatting defined by a formatter, on the other hand oe-stylize.py does not seem to be up to the task yet, like rustfmt, prettier or clang-format are.

I will close the PR for now. Maybe some day we will have an appropriate auto-formatter.