Synapse option to re-auth (or at least refresh-token-cycle) when user changes IP address

This issue has been migrated from [#11650](https://github.com/matrix-org/synapse/issues/11650).

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In order to help guard against someone's access_token getting stolen, it might be nice to require that access_tokens are refreshed whenever an access_token pops up on a new IP address - thus ensuring that an attacker will also have had to have intercepted the refresh_token too.

We could also have an option to do a soft logout whenever a user's IP address changes, for maximum paranoia.