Improve handling for changing email of invited users

[sgiehl]

Description:

Matomo has the possibility to invite new users. When a user is invited an email with an activation link will be sent to their email address.

The details of a user, who has not yet confirmed their invitation, can already be changed by the super user. This also includes the initially set email address.

This PR improves the handling if the email address of an invited user is changed.

When this happens, the previous invitation link will be invalidated and a fresh invitation will be sent to the new email address.

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

[michalkleiner]

The mechanism works as expected. I'm not 100% sure on the wording of the notification as it looks like we are cautioning against something that may not even happen. I was actually expecting to have a confirmation dialog explaining the mechanism only when the email was changed, asking whether the superadmin wanted to continue. We might be alarming too many people as it is now. It's just my perception, should we consult this with product? Or merge it as is and do a follow up ticket that we will never get to?

[sgiehl]

@michalkleiner I initially tried to extend the password confirmation to add the text in case the email was changed. But due to the way how the vue code is designed this is not fully possible. If you e.g. add a char and remove it again, that can't be detected.
But having more thoughts on that right now: Actually there isn't anything else than the email you can change for an invited user, as the password can't be set in that case. So guess we could simply always show the additional info in the confirmation for invited users. I'll try to change that quickly.