UI: Assign Instance Group to Domain/Account during Creation

### The required feature described as a wish

As an Admin or Operator, I would like to be able to Instance Group to Domain/Account in the UI. Currently the only way to do this is by logging into a user in account that you want the instance group to be created in.

Start by locating the UI entry point for creating an Instance Group and inspect how Domain or Account context is currently selected. Confirm the existing creation flow and permissions before defining the change. Done means an Admin or Operator can assign the Instance Group to a Domain or Account during creation without logging into that account.

Written by the indexing model from the issue text.