Add managed identities support to RG setup scripts

[eujing]

trafficstars

• Creates the managed identity (MI) in the specified RG. If existing, operation is idempotent.
• Assigns the MI as a user-assigned MI to the created control VM
• Grants the MI required roles for usage with the storage account file shares.

TODO:

• [x] Add support to the powershell script too.
• [ ] Consider MI access to the results DB too (part of incoming security wave requirements).