1779 single subscription scenario fails

[arjenhuitema]

Overview/Summary

This resolves a deployment issue occurring when deploying to a single platform subscription. The AMBA template received incorrect parameters, which mistakenly directed it to deploy to a standard management group structure.

This PR fixes/adds/changes/removes

1. Updated parameters that define the assignment scope for Management, Identity, and Connectivity policy initiatives within a single-platform subscription setup.
2. Now, setting the single platform subscription parameter in the AMBA Management Subscription parameter when deployed in such a configuration.

Breaking Changes

None

Testing Evidence

Please provide any testing evidence to show that your Pull Request works/fixes as described and planned (include screenshots, if appropriate).

Single platform management group deployment

Standard deployment

Testing URLs

Azure Public

As part of this Pull Request I have

• Checked for duplicate Pull Requests
• Associated it with relevant issues, for tracking and closure.
• Ensured my code/branch is up-to-date with the latest changes in the main branch
• Performed testing and provided evidence.
• Ensured contribution guidance is followed.
• Updated relevant and associated documentation.
• Updated the "What's New?" wiki page (located: /docs/wiki/whats-new.md)

[Springstone]

LGTM