Add filter support for pull requests.

[NicolasBonduel]

Hello,

It would be great if we could have the same thing for filtering PRs.

Thanks for your work!

[zacherkkila]

Yeah that is a good idea, not sure when I will get to it here but I will add that in

[sancarn]

Would be really useful for -label:dependencies to get rid of all the dependabot bumps.