Add Runtime Version to Stack.yaml

[EnriqueL8]

Is your feature request related to a problem? Please describe.
In each stack, the runtime version used is only defined in the FROM line whithin the Docker image.

Describe the solution you'd like
For better traceability, we could add this information into the stack.yaml as a language-version or runtime-version field. Which is then used by the CLI to add corresponding metadata through labels to the stack image. We may need to update each stack manually, and release a new version. We would need to document this change for new and current stack creator/maintainers.