Issue 1479: Check that usernames are not literals

[ms-sambell]

trafficstars

PR Summary

Adding code to verify if the resource type: Microsoft.Resources/deployments contains a property for adminUsername and what it's type is.

Fixes #1479

PR Checklist

• [ ] PR has a meaningful title
• [ ] Summarized changes
• [ ] Change is not breaking
• [ ] This PR is ready to merge and is not Work in Progress
• Rule changes
  • [ ] Unit tests created/ updated
  • [ ] Rule documentation created/ updated
  • [ ] Link to a filed issue
  • [ ] Change log has been updated with change under unreleased section
• Other code changes
  • [ ] Unit tests created/ updated
  • [ ] Link to a filed issue
  • [ ] Change log has been updated with change under unreleased section

[ms-sambell]

@BernieWhite @ArmaanMcleod

Hey gents, I got a little stuck when trying to write this. For the previous rules I had some examples to cheat off. I'm not quite sure how to use PsRule specific assertion methods to verify the properties of a value assigned to a property.

Any tips / feedback / examples would be great.

[ms-sambell]

@BernieWhite @ArmaanMcleod - hey team, can I please get a review