Ability to add/remove user in a specified user directory

Currently, if multiple user directories are defined in Confluence, the Add/Remove User operations will only be applied to the top directory. If the top directory cannot be modified via Confluence (e.g. LDAP read-only directory), the operation will fail.

In order to add a user to the Confluence Internal Directory in this configuration, one would need to swap the directory order in Confluence Admin > User Directories, add the user, then swap it back. This procedure is inconvenient and oftentimes confusing.

Instead, Confluence should automatically add the user to the Internal Directory if no other directory can be modified, and give a choice to the user if there are multiple possible directories (e.g. 'Confluence Internal Directory' and 'Internal with LDAP Authentication').

This behavior would also be more consistent with the user management behavior in JIRA.