Fix sign job failure with Commands.Common.Websites

[cormacpayne]

Description

Add a reference to the Commands.Common.Websites project in the Stack.sln file to potentially fix sign job

Checklist

• I have read the Submitting Changes section of CONTRIBUTING.md
• The title of the PR is clear and informative
• The appropriate change log has been updated
• The PR does not introduce breaking changes
• If applicable, the changes made in the PR have proper test coverage
• For public API changes to cmdlets:
  • the changes have gone through a cmdlet design review
  • the cmdlet markdown files were generated using the platyPS module

[cormacpayne]

Sign job: https://azuresdkci.westus2.cloudapp.azure.com/job/ps-sign/651/