Make delete-management-groups.bat script more robust

[skeeler]

Is your feature request related to a problem? Please describe.
The original delete-management-groups.bat script worked well with the original management group hierarchy that imposed a hierarchical structure on the management group IDs. Once we added the new management group hierarchy JSON variable in the environment YAML configuration files, it became possible to configure management group IDs that did not need to follow the previous convention since the parent-child relationships are explicitly stated in the JSON structure. As a result, newer deployments not following the original management group ID naming convention will not work with the original script.

Describe the solution you'd like
Rewrite the delete-management-groups.bat script to support the newer flexible IDs for management groups, and while we're at it, fix issues with any custom role definitions at management group scope and custom role assignments at subscription scope that would result in errors or orphaned object references when related management groups are removed.