Modules system: callback for `on_login` which includes the deviceName from the client

This issue has been migrated from [#10487](https://github.com/matrix-org/synapse/issues/10487).

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I'm looking at https://matrix-org.github.io/synapse/develop/modules.html and don't see a callback for `on_login`. I'd like a callback that contains the `deviceName` for the user logging in.

cc @babolivier @chagai95

Start with the modules documentation at modules.html and investigate how login-related callbacks are exposed. Define the requested on_login callback behavior and how the client's deviceName should be passed to it; done means the documented callback provides that value to modules.

Written by the indexing model from the issue text.