Restart button works only for tasks created by the current logged-in user

[Amdrel]

From another thread with @Don-vip

• the restart button works only for tasks created by the current logged-in user. For those like Amdrel and me who have admin privileges in the UI, we should be able to restart failed tasks created by other users
• we don't see on which encoding instance the task was running, it's a guessing game right now, it should be displayed somewhere

For normal users, they have no idea of the current load. The frontend should display, and refresh, how many tasks are currently processed / waiting before their own, so that they can see when the system is just busy and not stuck. Sometimes users cancel theirs tasks because they think it's stuck, while there is simply someone that created many tasks before them.

Phabricator ticket: T410732