Require password confirmation when inviting a user in UI

[sgiehl]

Description:

This also adds the requirement to provide a password confirmation to the method UsersManager.addUser, but as the method in not longer used in the UI, this will only prevent it being "misused" with a session auth.

Review

• [ ] Functional review done
• [ ] Potential edge cases thought about (behavior of the code with strange input, with strange internal state or possible interactions with other Matomo subsystems)
• [ ] Usability review done (is anything maybe unclear or think about anything that would cause people to reach out to support)
• [ ] Security review done
• [ ] Wording review done
• [ ] Code review done
• [ ] Tests were added if useful/possible
• [ ] Reviewed for breaking changes
• [ ] Developer changelog updated if needed
• [ ] Documentation added if needed
• [ ] Existing documentation updated if needed

[bx80]

Not sure why one of the UI screenshots is out by one pixel, I'll update it again just to be sure.