Room drawer garbage collection: Automatically leave after a period of inactivity

### Your use case

#### What would you like to do?

* The user should be empowered to focus their activity on Matrix and to not be obliged to maintain presence where their contribution is low

#### Why would you like to do it?

* The room drawer can get full over time as many people join a lot of rooms, but never leave them
* https://en.wikipedia.org/wiki/Continuous_partial_attention
* https://en.wikipedia.org/wiki/Attention_economy
* https://en.wikipedia.org/wiki/Bystander_effect
* Notifications within interesting rooms may get swamped by random activity within rooms of less interest to the user
* https://en.wikipedia.org/wiki/Information_overload
* Some of the bridges already do this without the user having an option to influence this

#### How would you like to achieve it?

* The user must be able to alter new account settings
* Their clients should automatically leave rooms which are of little use to them
* The inactivity period may default to 30 days
* The interpretation of activity may be chosen to mean either the user opening the given room (most recent read receipt), fully reading through the chat log or sending events to the room (messages or reactions)
* It must not apply to rooms where the user has elevated privileges - i.e., where others are counting on them to stand by to help combat future abuse
* It must be handled in a special way if the user has not logged into their account for an extended duration. They may be either greeted with a room overview dialog or their inactivity counters could be reset.
* It must be handled in a special way when nobody posts events to a given room for that duration of time. It may have a user setting to leave such inactive rooms as well.

### Have you considered any alternatives?

* The home server of the respective user could have a plugin to implement this logic
* A hosted bot or a home server of any moderator could implement this logic via kicking

Both are much more involved, less polite and would be less plausible to become a mainstream feature usable by any user on demand.

### Additional context

https://en.wikipedia.org/wiki/Well-being

### Are you willing to provide a PR?

No

The issue names no repository files, tests, or entry points. Start by identifying which Element client owns account settings and room-membership behavior, then clarify the inactivity definition, privilege exceptions, and handling of dormant accounts before defining acceptance criteria.

Written by the indexing model from the issue text.