Add a 'referenced date' and/or an 'updated' date to merge requests in issues

Description

Looking through issues, I can see referenced MRs, but it's not clear how old they are or the last activity on them without visiting each one and looking at the last activity. Adding this date would be a quick way to see whether or not an issue is stale or not.

Proposal

Something like the following (quick mockup):

Reference date would be the date the MR was mentioned. Updated date would be the date of the last comment (and/or activity?) on the MR.

~"feature proposal"