This adds tests for `/profile`. Also, as a first change in this regard, refactors the methods defined on the `UserInternalAPI` to not use structs as the request/response parameters.
Adds tests for - `/devices` - `/delete_devices` (also adds UIA)
Fixes https://github.com/matrix-org/dendrite/issues/2980
As discussed yesterday, a first draft of merging the keyserver and the userapi.