Consider making `inhibit_login` default to true for appservices

Nobody has claimed this yet.

https://adoring-einstein-5ea514.netlify.app/client-server/#post_matrixclientr0register `inhibit_login`

>If true, an access_token and device_id should not be returned from this call, therefore preventing an automatic login. Defaults to false.

Appservices should not use the access token returned by /register and instead use the token provided in their registration. The device_id is similarly not important for most bridges, and should be off by default. If bridges are E2EE capable, then device_ids and access tokens may be useful and so the bridge can opt in to get this information.

Doing this would save resources and time on the homeserver. However, doing so would lead to backwards incompatibilities with existing bridges which rely on this behaviour (they would need to provide inhibit_login in their registration requests).

Start with the Matrix client-server registration endpoint linked in the issue and review the `inhibit_login` behavior for appservices. Assess the compatibility impact on existing bridges and define the spec change and opt-in behavior needed for E2EE-capable bridges; done means the default and migration requirements are unambiguous.

Written by the indexing model from the issue text.