Fix doc link for parameter description

[stalejohnsen]

Overview/Summary

Fix dead link in description of parExcludedPolicyAssignments

This PR fixes/adds/changes/removes

1. Change link url in description to the correct destination in wiki.

Breaking Changes

Testing Evidence

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)
• Updated relevant and associated documentation (e.g. Contribution Guide, Module READMEs, Wiki Docs etc.)
• If relevant, created or updated Code Tours here

[jtracey93]

/azp run validateazcloud

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