Ability to automatically kick out idle devices

[ara4n]

Some users may want to kick out devices which haven't been used in N days and force the user to log back in, ensuring that if the device is compromised the attacker won't be able to read more than N days of history from the point of compromise.

See https://news.ycombinator.com/item?id=28513878

[aaronraimist]

Is that was session_lifetime does? https://github.com/matrix-org/synapse/blob/develop/docs/sample_config.yaml#L1180-L1189 or does that timer not get reset if the device stays active?

[anoadragon453]

It doesn't appear that the counter for session_lifetime is reset upon device activity, but this may be a nice addition to add to the feature.

[bradtgmurray]

Is this delete_stale_devices_after ?

[DMRobertson]

Related: #14038