Add markdown workflow to trigger a spotless check

[wmontwe]

This fixes #7216

[cketti]

Can we prevent this workflow from running when a PR is also triggering the Android workflow (e.g. when a .kt file and an .md file was changed). Otherwise both workflows will check Markdown files.

[wmontwe]

Looking at the docs, it's not straight forward. There is an example to including and exclude paths but that will still trigger when there is a match on **.md. There is also a job if condition, but that goes beyond my knowledge. So maybe?

Edit:

From the docs:

Note: The order that you define paths patterns matters:

A matching negative pattern (prefixed with !) after a positive match will exclude the path.
A matching positive pattern after a negative match will include the path again.

[wmontwe]

But the quality check could be a standalone workflow, always checking everything, and the android one just assembles and tests the app code base.

[cketti]

Potentially checking Markdown files twice is better than not checking them at all 👍