Align organization user type terminology in add users modal

What does this MR do and why?

Update the copy on the user type in the organization invite modal. Align it with the copy we use on the edit page.

References

• #629294 (closed)

Screenshots or screen recordings

Edit Page (Reference)	Invite modal

How to set up and validate locally

1. Start GDK and navigate to an organization's admin users page.
2. Click the "Invite user" button to open the modal.
3. Confirm the "Organization user type" label and the dropdown options now read "Organization regular user" and "Organization administrator".

MR acceptance checklist

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