Identify and ignore duplicate built-in policies from MDfC default assignment

This issue is about looking through the policies definitions in https://github.com/Azure/PSRule.Rules.Azure/blob/main/tests/PSRule.Rules.Azure.Tests/Policy.assignment.json to identify any policies that are duplicates of existing rules within PSRule for Azure.

Duplicates will:

- Have documentation updated to identify that they are equivalent to a specific Azure Policy.
- Be added to a built-in exclusion list that would be implemented in #1730.