Support net 7

[JustinWilkinson]

The changes in this PR are as follows:

• Add support for .NET 7.

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

• [x] Tested my code end-to-end against a live Azure subscription.
• [x] Updated the documentation in the docs folder for the affected changes.
• [x] Written unit tests against the modified code that I have made.
• [x] 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.

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

webApp {
      name "my-web-app"
      runtime_stack Runtime.DotNet70
}