This reworks the assignment of the default role at login. The assignment
now only happens if settings service is reachable and the current user
does not have an assignment yet (we check for the NotFound status).
If the settings service returns an error other than 404, the
GetUserByClaims() (and with it the authentication) will also error out.
Closes: #3900
When removing the accounts service we lost the user autoprovision
feature. This re-introduces it. When autoprovisioning is enabled (via
PROXY_AUTOPROVISION_ACCOUNTS, as in the past) accounts that are not
resolvable via cs3 will be provsioned via the libregraph API.
Closes: #3540
