Add "Last Activity" column to CSV export in /admin/users

Problem

Administrators use the /admin/users page to manage users, including tracking their latest activity so they can plan license allocation for future users. Admins will also use this page to export CSV data on GitLab usage to report to their business stakeholders.

In gitlab-foss#43681 (closed), we added a "Last Activity" column to the user admin page. Users can be exported to CSV from there, however the "Last Activity" column is not included in the CSV export.

This makes it difficult for administrators to report their user count accurately to their leadership.

Workaround

This information can be gathered from the API as described in this documentation. That said, this is not a realistic workaround for two reasons:

• In order to gather this information, an administrator must use their Personal Access Token, which poses a risk to have a separate process to authenticate to gather this information.
• Users who are supporting/administering GitLab user management might not be technical users and thus will not be able to use the API to collect this information.

Suggestion

Include the "Last Activity" column in the CSV export from /admin/users.