Optionally make users created via the API set their password

What does this MR do?

This merge request makes it possible to specify that a user created via the API should receive an email asking them to set a password, rather than set a predefined password and not alert the user.

Are there points in the code the reviewer needs to double check?

Why was this MR needed?

In order to properly automate user creation, it is convenient not to have to communicate about passwords at all, but leave this up to the user.

Screenshots (if relevant)

Does this MR meet the acceptance criteria?

• Changelog entry added
• Documentation created/updated
• API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #1051 (closed) (Yes, that's an old one!)