core_user_external::get_users_by_field() missing some fields.

There are a few fields missing from the result when calling this function.

One example that is affected is this webservice, see: http://moodle.test/admin/webservice/documentation.php then expand core_user_get_users_by_field

One of the fields listed there is the 'auth' field, which is missing because get_users_by_field() did not provide it.

Please note that in Moodle 29 we could get the auth field (and others) using the get_users_by_id() which was deprecated and removed.

I am marking this as a BUG because scripts that relied on get_users_by_id() may not work on Moodle 31 using the get_users_by_field() replacement.