Only show joins, etc. for users that have been recently active

[mythmon]

Is your suggestion related to a problem? Please describe.
The messages about users joining, leaving, changing avatars, etc, are often noisy, especially in quieter rooms. Just turning them off can work, but can leave you in the awkward situation of talking to someone who has left, or not realizing that someone has changed their name.

Describe the solution you'd like
It would be useful to see joins and parts only for users that have recently interacted with the room, or been interacted with by others. For example if a user sends a message, or if someone @ mentions them.

Notably, if someone joins the join message will not be shown. Then if they send a message within a short time period, the join message is re-shown. The filter works both forwards and backwards in time.

Describe alternatives you've considered
It may be possible to build a UI that shows all meta information about the members of a room in a way that doesn't get in the way of the conversation. Then there would be no need to hide them.

Additional context
Weechat has a feature like this builtin called smart filter

[HansJK]

This should happen automatically when a room have over a certain number of members. Would love to see this happen.

For Communities 2.0
I have a fairly big Discord server, and as everyone knows, Discord operates with multiple channels instead of just one chat room, and everyone is a member of the Server and not the individual channels. And there you would usually just have a dedicated spam or info channel where all this kind of information would go.
So when communities have been rewritten and we have communities 2.0, it should be possible have a dedicated room/channel for showing joins and etc.

[t3chguy]

This should happen automatically when a room have over a certain number of members

Doing things magically based on a random threshold causes more confusion than it solves.

[HansJK]

Doing things magically based on a random threshold causes more confusion than it solves.

Fair enough.

[MadLittleMods]

Related to #337 and element-hq/element-web#5479