[user_accounts] All sites in drop down instead of user's sites

[CamilleBeau]

Describe the bug Written in testplan:

15. Verify that if the editor does not have permission 'Across all sites add and edit users' then the site drop-down list is populated with the editor's associated sites, otherwise all sites are displayed.

Editor with the permission "User management", but not "Across all sites add and edit users" is able to see all of the sites in the drop-down including the sites that are not their own.

To Reproduce Steps to reproduce the behavior (attach screenshots if applicable):

1. Make a user with the permission "User management" and WITHOUT permission "Across all sites add and edit users"
2. Select some but not all sites for this user (e.g. Montreal, Ottawa only)
3. Login with this user and go to the user accounts page.
4. Notice that all of the sites are in the site drop-down

[laemtl]

Will be solved by #6836 (in progress and blocked by #6945)

[CamilleBeau]

Resolved