Add possibility to create user in the Remote User mode Auth.

[lwyszomi]

This fix gives a possibility to create user in the Remote User Auth. I know that we have open discussion about the same issue in the LDAP mode (#18545), but in the Remote User mode I think this option should be available.

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[potiuk]

I think some common approach here should be worked out. I am for adding it, but I am not as "deeply" in the rules and configuration - I believe for the new UI we are porting FAB permission model to Airlfow. so maybe that's a good time to discuss and agree something there @ashb @jithimmins @bbovenzi @ryanahamilton ?

[kosteev]

@potiuk @jhtimmins Can you, please, review this fix/change one more time.

[jhtimmins]

This is a sensible change, and looks like it was supported in the original version of UserRemoteUserModelView in Flask Appbuilder.

https://github.com/dpgaspar/Flask-AppBuilder/blob/985b1b7c1d77d38e667199573455a4a3b6f40ac9/flask_appbuilder/security/views.py#L286

It shouldn't be necessary to modify _class_permission_name or class_permission_name_mapping though, since those values remain unchanged from the base class.

It may be tricky to test though. @kosteev or @lwyszomi can one of y'all verify that the change works as intended and that you can actually add a new user and then log in with that user?

[jhtimmins]

This change makes sense. Please see my comment for requested changes, in addition to the merge conflicts.

[lwyszomi]

@jhtimmins I duplicated both values from base Class to easly show that this is needed in the UserRemoteUserModelView. We have similar implementation in the CustomUserDBModelView one of the parameters are copy pasted for Mixin class, second is changed.

Change is already tested and all works fine.

[potiuk]

Hey @jedcunningham - I think that one should be easy to cherry-pick to 2.1.4 and it is a bit of regression (not entirely - this was a change in FAB rather than in Airflow). I marked it as 2.1.4 but maybe you can decide whether to cherry-pick it to 2.2.4 or not.