Show sole-owned groups in remove organization user modal

What does this MR do and why?

When removing a user from an organization, show a list of groups that they solo own. This blocks their removal from the organization.

A follow up will be created to update the leave / self-remove modal as well.

References

• Closes #629289 (closed)

Screenshots or screen recordings

How to set up and validate locally

1. Enable ui_for_organizations and org_experimental feature flags
2. Go to /o/<organization>/admin/users
3. Attempt to remove a user who is a solo owner of a group in the organization.

Tip: You may ask DAP or any agent that you have to create the mock data.

MR acceptance checklist

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