Per category default watch state (and a way to reset everybody to that state)

NodeBB version: 1.12.2

Feature Request

• Add a feature to each category that allows a default setting for watch state.
• Add a checkbox that allows the user to override the default or not.
• Allow admin to press a button to overwrite all user's current setting for that category (or just provide a script in the docs or something that we can run to do this).

Note: I know we currently have a setting that is global for all categories. For my use case it's not super helpful.

Motivation: there are certain types of forums that have categories that create a lot of noise. In particular, gaming site where people "play by forum." Any feature of the forum that relies on watched categories gets "spammed" by these game status posts.