feat: Add nested dictionary formating check

[sblaisot]

This pull request add a check on proper nested dictionary over-indentation as advised in https://docs.saltproject.io/en/latest/topics/troubleshooting/yaml_idiosyncrasies.html#nested-dictionaries

It adds Rule 219 (which seems to be the first never-used 2xx rule number). Feel free to change rule number if needed.

This fixes #282

[jbouter]

Hi again @sblaisot!

Thanks so much for your PR. Looks like you ticked all the right boxes on your PR as well! We'll try to do a code review as soon as we can, and integrate this new feature into our next release if it passes :-)

[matthijswendelaar]

Thanks for the PR @sblaisot! The PR looks good overall, I have made a few suggestions to avoid some false-positives and have correct versioning of the rule.

[sblaisot]

Thanks for review @matthijswendelaar
All comments addressed

[matthijswendelaar]

Thanks for the changes @sblaisot, I made a single suggestion to revert back to your original of 2 spaces of over-indentation required, instead of only 1 space of over-indentation required that I suggested.

After that the PR can be merged.