Support pinning dotnet-version as `"latest"`

[aep-sunlife]

Description:

As a developer, I want to create a GitHub Actions job that tests my .NET projects against floating, bleeding edge .NET versions. For comparison, workflows for other languages like Go support this with the "latest" version value.

Justification:

Today, I do not see an option to let the .NET version automatically target the latest stable .NET release version. Which breaks efforts at futureproof testing, with each new major release of .NET.

[aparnajyothi-y]

Hello @aep-sunlife, Thank you for creating this feature request. We will investigate it and provide feedback as soon as we have some updates.