Add a GitHub action for periodically running vale

[k-dimple]

No description provided.

[SecondSkoll]

I think this should run on PR, as Vale doesn't currently run alongside our other checks.
I believe it should also be in sp-files/.github/workflows.
@evilnick to check my thoughts though :)

[evilnick]

Thanks. Yes, it should go in the sp-files/.github/workflows so it gets copied when a new project is made
I think it's fine to run on a schedule to satisfy the metric requirement, even if we aren't actively recording it. Adding vale checks to the doc PR checks is probably a separate card

[k-dimple]

@SecondSkoll and @evilnick thanks for the reviews, I have moved it under the sp-files folder.