Add get_menu_items in auth manager interface to extend the menu

[vincbeck]

Part of #47457.

Define a method in the auth manager interface get_menu_items so that auth managers can extend the menu if needed. By default, it returns an empty list.

I defined the method in the Fab auth manager to add 5 links to the menu:

• List of users
• List of roles
• List of actions
• List of resources
• List of permissions

The return value of get_menu_items for FAB auth manager is:

[
	MenuItem(text = 'Users', href = '/auth/users/list/'),
	MenuItem(text = 'Roles', href = '/auth/roles/list/'),
	MenuItem(text = 'Actions', href = '/auth/actions/list/'),
	MenuItem(text = 'Resources', href = '/auth/resources/list/'),
	MenuItem(text = 'Permissions', href = '/auth/permissions/list/')
]

Once this PR merged, get_menu_items return value needs to be passed to the front-end and then these menu items can be added to the menu (I recommend to put them under a same category like "Auth").

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[vincbeck]

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