Watch individual posts

**Is your feature request related to a problem? Please describe.**
Currently there is no easy way to see updates for specific posts and I’d like to be able to subscribe to newly created comment events.
A simple example: user A creates a post which asks for advice on a given problem.
User B is also interested in solving this problem but will have to manually check for updates on said post.

**Describe the solution you'd like**
Add an additional `Watch` button which will subscribe to comment events for the current post.
Whenever a new comment is created, it will send a notification to the subscribed users and also show up in their inbox, perhaps in a separate category if necessary.

**Describe alternatives you've considered**
Currently I manually save posts and periodically check for new comments which isn’t ideal.

**Additional context**
This feature is similar to how a GitHub repository can be watched for specific events.
I’m not sure if events other than newly created comments would be interesting, so I’ll limit the scope of my feature request to that.