Allow to update user info on Upstream Login

[matrixbot]

This issue was originally created by @n0emis at matrix-org/matrix-authentication-service#3117.

For example when running a deployment with an upstream OIDC-Provider and with changing Displayname/Mail disabled, it would be good to have the ability, to automatically update these Infos from the UserInfo-Token instead of only doing this on the initial linking.

[matrixbot]

This comment was originally posted by @akoyaxd at matrix-org/matrix-authentication-service#3117 (comment).

This is especially painfull, if you already use sso with synapse and migrate to MAS, as it does not migrate E-Mail but then requires users to manually enter their E-Mail while and not importing it from SSO.