Refactor ARM template expression to use a simpler template function t…

[OutOfScopeia]

…o achieve the same effect. Updated the sample JSON it is tested against as well.

This PR closes #

The changes in this PR are as follows:

• Uses subscriptionResourceId() instead of subscription(), as a result doesn't need concat() and ends up being simpler
• Updates accordingly the sample file this functionality is tested against

I have read the contributing guidelines and have completed the following:

• [X] Tested my code end-to-end against a live Azure subscription.
• [ ] Updated the documentation in the docs folder for the affected changes.
• [X] Written unit tests against the modified code that I have made.
• [ ] Updated the release notes with a new entry for this PR.
• [X] Checked the coding standards outlined in the contributions guide and ensured my code adheres to them.

If I haven't completed any of the tasks above, I include the reasons why here:

Below is a minimal example configuration that includes the new features, which can be used to deploy to Azure:

[ninjarobot]

Thanks for the contribution @OutOfScopeia. This is included in the 1.7.27 release and available on nuget.