Follow conversation by push notifications and notifications global settings.

This is related to an observed behaviour while testing this PR here

The new feature allows to enable push notifications for comments on a post.

Reporting the issue description from the PR:

1. I enabled in-app push notifications for conversation as mentioned in the instructions, but did not receive them in an instance when I had notifications disabled for the comments on my own (atomic) site under the Notifications tab. Once I enabled the setting, I started receiving them.
2. I disabled notifications for conversations, yet was able to receive them when someone commented on the thread. Comments needed moderation, once approved, new comments from the same user were displayed as remarked comments under the Notifications tab.

The reported issue was noted on an atomic site owned by the user that was activating the push notifications, and it seemed initially that the global notification settings for a site that you own could affect the behaviour preventing the user to actually get notifications for comments on that desired post.

Namely these are the settings we were looking into:

I was not able to reproduce the issue on my side and we verified with @ashiagr that the issue was not happening on her end anymore as well regardless the Notifications global settings status.

It seemed fair to report in an issue anyway in case something similar could happen. Also it's possible we would want to review the general behaviour of the feature linking to these settings in an iteration 2.

cc @ashiagr, @mattmiklic, @aerych

Start by reviewing PR 15459 and issue 15460, then examine the notification and global Notifications settings described here. Test conversation push notifications with those settings enabled and disabled, including moderated comments. Done means the interaction is understood and the intended behavior is confirmed or a reproducible defect is documented.