New parameter for Alzdefaults exclusions

[stalejohnsen]

Overview/Summary

This PR will add flexibility to exclude specific policies from ALZ Default Policy Assignments module via the new parameter parExcludedPolicyAssignments. This will help organizations that need to deviate from some of the ALZ reference implementation policies, but at the same time wants to keep the ALZ Default Policy Assignments module as is for easier upstream updates.

This PR fixes/adds/changes/removes

1. New parameter parExcludedPolicyAssignments in ALZ Default Policy Assignments module
2. New wiki section in AssigningPolicies.md to describe how to use the exclusion parameter.

Breaking Changes

1. The new parameter is optional only.

Testing Evidence

1. First test excluding all default policy assignments
   
2. Deployment success with no policy assignments
   
3. Second test excluding 6 specific policy assignments
   
4. Deployment success with all policy assignments excluding the 6 from parameter
   

As part of this Pull Request I have

• [ x ] Read the Contribution Guide and ensured this PR is compliant with the guide
• [ x ] Ensured the resource API versions in .bicep file/s I am adding/editing are using the latest API version possible
• [ x ] Checked for duplicate Pull Requests
• [ ] Associated it with relevant GitHub Issues
• [ x ] (ALZ Bicep Core Team Only) Associated it with relevant ADO Items
• [ x ] Ensured my code/branch is up-to-date with the latest changes in the main branch
• [ x ] Performed testing and provided evidence.
• [ x ] Updated one or more of the following tests (if required)
  • Unit
  • Linting
  • E2E (End-To-End)
  • ValidateAzCloud (Base validation in Azure Cloud)
  • ValidateMcCloud (Base validation in Azure China Cloud)
• [ x ] Updated relevant and associated documentation (e.g. Contribution Guide, Module READMEs, Wiki Docs etc.)
• [ x ] If relevant, created or updated Code Tours here

[jtracey93]

/azp run validateazcloud

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[jtracey93]

/azp run validateazcloud

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[jtracey93]

/azp run e2e

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[jtracey93]

/azp run validateazcloud

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[jtracey93]

/azp run e2e

[azure-pipelines]

Azure Pipelines successfully started running 1 pipeline(s).

[jtracey93]

LGTM