ms_graph: get identity from /v1.0/me

Instead of trying to read the user identity from /v1.0/me/drive, get it from /v1.0/me where it is guaranteed to be the signed in user.

See: https://learn.microsoft.com/en-us/graph/api/user-get?view=graph-rest-1.0&tabs=http#example-2-signed-in-user-request

closes #327 (closed)