Note that owner must export project for user mapping to work

What does this MR do and why?

Notes that exports must be generated/downloaded by a project or group owner for user mapping to work in the project export/import > user mapping docs.

Screenshots or screen recordings

• tree/project/project_members.ndjson from project export generated by project or group maintainer is empty.
• tree/project/project_members.ndjson from project export generated by project or group owner lists all the project or group members, along with their usernames and email addresses (if public)

How to set up and validate locally

Requirements:

• 2 self-managed instances (running GitLab 14.6 or newer)
  • Instance A = instance where export will be generated
  • Instance B = instance where project export will be imported
• create 3 users on each instance with email set to public
  • root = admin (email admin@example.com)
  • bob = non-admin user (email bob@example.com)
  • mary = non-admin user (email mary@example.com)

1. On Instance A, have root user create a project and grant bob the Maintainer role for that project
2. Log in as bob on Instance A and create an issue or MR in that project assigned to bob
3. Log in as mary on Instance A and create an issue or MR in that project assigned to mary
4. Create two project exports on Instance A - one created using the root user, and the other created by bob user
5. (validate locally) Extract the export archives and view tree/project/project_members.ndjson - note that the export created by the Owner has all the user information, and export created by the maintainer does not
6. (validate in GitLab) Import both project exports to Instance B as the root user. Verify that the export created by root user correctly assigned bob and mary to any issues/MRs that were assigned to bob/maryon Instance A. However, the export created bybobdid not correctly map issue/MR assignees tobob/mary`.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• I have evaluated the MR acceptance checklist for this MR.