Allow network admins to manage application passwords for all users

[Sukhendu2002]

Trac ticket: https://core.trac.wordpress.org/ticket/60029

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[SirLouen]

These tests are interesting but the only question that comes to my mind is that I can't see with these tests is that the actual method WP_REST_Application_Passwords_Controller::get_user that is causing the issue is not being asserted. So the test is failing because of an error, not because of a wrong assert.

[SirLouen]

@Sukhendu2002 can you review the test?