[Request] Please consider channel based visibility options for thread replies

Description:

Current global thread reply options are not very flexible for different types of discussion.

In official company discussions it is important that messages do not flood the main channel view and discussion remains confined. Important company messages would not remain on the screen very long otherwise.

On more relaxed channels people cannot find interesting discussions based on the possibly less meaningful first messages of the thread alone.

Going off-topic in discussions is part of our human nature, in good and bad. Current solution does not cover the needs well when that good happens.

Also there is such thing as anxiety for being the first one to say something in the room. This also stifles discussion.

Steps to reproduce:

1. You need 500+ users on the RC instance
2. Create a channel for official company speak for all people
3. Create another channel for general chatter for all people
4. Under admin settings choose default thread reply visibility as either Unselected by default option to prevent flooding of the official channel.

Expected behavior:

On the official speak channel people are serious. There is no chaos of chatter. No-one is laughing. Ever.

On the general channel people chatter about happily. New ideas emerge from getting opposite views to their own viewpoints raised in the discussions. There is laughter and sunshine. Occasional fight happens, but those end in hugs.

Actual behavior:

Discussion on the general chatter channel is dead too. Occasional tumbleweed passes by. You feel your mouth drying up and you move on to other things. There will not be any new ideas, stagnation prevails.

Server Setup Information:

• Version of Rocket.Chat Server: RC 5.4.2
• Operating System: RHEL8
• Deployment Method: tar
• Number of Running Instances: 10
• DB Replicaset Oplog: Yes
• NodeJS Version: 14.19.3
• MongoDB Version: 4.4

Additional context

I'm actually very serious about this. We are seeing in effect how very limited thread visibility options for different type of discussion causes corporate discussion culture to change for more closed instead of more open. Sorry for persisting with this. :)

The issue names no files, tests, or entry points. Begin by clarifying the channel-specific visibility rules and checking how the existing global default setting should relate to them; done means an agreed implementation scope and behavior for official and general channels.