Export-BicepChildResource throws with "access denied" to list roleAssignment

[SebastianClaesson]

Describe the bug
Export-BicepChildResource throws an error saying the credentials used do not have access to list roleAssignments.
Refreshed credentials in both Az CLI and PowerShell, after checking out appropriate role.

To Reproduce
Steps to reproduce the behavior:
Run the Export-BicepChildResource with a subscription or resource group as the ParentResourceId.

Such as:
Export-BicepChildResource -ParentResourceId "/subscriptions/c5f27640-57b7-79f1-9896-cb4b49217632"
Export-BicepChildResource -ParentResourceId "/subscriptions/c5f27640-57b7-79f1-9896-cb4b49217632/resourceGroups/rg-test-infra"

Expected behavior
Return all Child resources from that subscription or resource group.

[PalmEmanuel]

Related to the work planned for #258 where we would likely take a dependency on AzAuth and rework the current authentication implementation which isn't very transparent.