Port module to the new interface

Synapse introduced new generic modules system in v1.37.0. For more details see:
- https://element-hq.github.io/synapse/latest/upgrade.html#upgrading-to-v1390
- https://element-hq.github.io/synapse/latest/modules/porting_legacy_module.html
- https://element-hq.github.io/synapse/latest/modules/password_auth_provider_callbacks.html