Prioritize Organisation Users in invitation modals
## Problem
On GitLab.com, when inviting a new member to a group/project, we currently list all users of GitLab.com. It would be more user friendly to restrict these invitations to Organization Users and/or prioritize them in the invitation modal.
## Proposal
Here are some options that we should validate further:
- Prioritize Organization Users when listing users in invitation modals for groups and projects. Perhaps they could be listed first as `Organization Users` followed by `GitLab.com Users`.
- Restrict invitation modals to display only `Organization Users` altogether, for example via a setting. For Organizations that want to ensure that group and project `Owners` do not invite external users, this might be desired.
- Let users select while working in the modal whether they want to focus only on Organization Users.
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