Allow root account to manage other users' synchronizations

[fflorent]

Describe the problem to be solved

When #754 is finished (PR #5135), administrator accounts cannot manage other's users synchronizations.

Also maybe:

• to create synchronizations in behalf of the user

Describe the solution you would like

We'd probably want the admins to be able to manage other users' synchronization through the UI.

I think the main use cases would be:

• to see whether the synchronizations failed / succeeded / are running
• to delete bad synchronizations
• trigger a full synchronization

Some questions to be answered regarding the UI:

• where to place a menu item / button so they can go to the list of users' synchronization?
  • Maybe in the context menu of the users administration list [1]
• should the UI offer a create synchronization button?
  • this would probably require some Front rework
  • as the administrator can do this through the API, I don't think that's much important

[1] What I mentionned as "the context menu of the users administration list" is this one: