surface related entities in google groups forums

[tatianab]

Add the ability to surface related entities (similar to Gaby's related issues comments) as replies to google groups forum discussions. (This needs a careful evaluation before we decide whether to turn it on for any of our golang-* forums).

[hyangah]

This is an extension of the similar/duplicate issue feature. Since we are focusing on the issue management in this iteration, I am moving this to Backlog.