[BackOffice] Add a possibility to add a second admin account for connected instances

[ruslanbaidan]

Motive
Sometimes we receive requests to change the instance admin account.
The reason can be that the person doesn't work at the company anymore.
The current functionality does not allow to implement the change as well as deactivate the old admin account.

Solution
A Simple UI on the BackOffice side to be able to replace the admin account.
The details are store in a specific json file and used by ansible to do the job on a client side.