FEATURE: Add site setting to restrict ignore feature to trust level (PR #11297)

This adds a new min_trust_level_to_ignore site setting to allow admins to control the point at which as user is allow to ignore other users.

Screen Shot 2020-11-19 at 7 27 10 PM


I think we should make the name consistent with the other site setting? min_trust_level_to_ignore :arrow_right: min_trust_level_to_allow_ignore.

Sure, works for me!