A support for duration check linter

[purpleidea]

This seems like an easy and very helpful linter to add:

https://github.com/charithe/durationcheck

Related issue:
purpleidea/mgmt#494

Thanks!

[stale]

This issue has been automatically marked as stale because it has not had recent activity. It will be closed if no further activity occurs. Thank you for your contributions.

[purpleidea]

hi bot

[SVilgelm]

I really tried to add it, but it requires some changes in the durationcheck.

[SVilgelm]

I created a ticket in main repo: charithe/durationcheck#6