Incognito mode for large rooms like announcements room

### Your use case

### Display the room timeline only with messages.

Announcement rooms are used to send important notices/alert message to the members. Only the privileged users can send message and rest of the members can only read the message.
The audience members are not required to see the other members and the events like changed avatar, left room, read recipients, .....
The timeline should be clean only with messages.

### Why would you like to do it?
Right now the larger announcement rooms are filled with other normal members activities, and they are not expected to explore the other members list part of the announcement room.

### How would you like to achieve it?
m.room.custom.policy will be stored with key incognito and value incognito.enabled to enable the incognito mode.
This key/value will used in the client side to apply the policy.

### When Incognito mode is enabled below items are not displayed.
- membership events ,
- read receipts,
- list of members in the room. (only the moderator and above can see)

Settings:


Enabled Mode:


Disabled Mode: