Allow specification on NET Framework on slot for a webapp

[nkuzmincodat]

This PR closes #

The changes in this PR are as follows:

• Allows specification of NET Framework for a web app slot
• Adds .NET 8 member to Runtime

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

• Tested my code end-to-end against a live Azure subscription.
• Updated the documentation in the docs folder for the affected changes.
• Written unit tests against the modified code that I have made.
• Updated the release notes with a new entry for this PR.
• 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:

let slot =
  appSlot {
      name "warm-up"
      runtime Runtime.DotNet80
  }

[r30e]

The joy of currying means you don't need to declare the lambda here, you can just use function directly which has a "dangling" second argument which is left to Option.map to fill in.

Suggested change

	NetFrameworkVersion = this.Runtime |> Option.map (fun r -> r |> function
	NetFrameworkVersion = this.Runtime |> Option.map (function