Have scaleDown operation shutdown the instance rather than killing it

[peterbean410]

Right now, the scaleUp operation takes about 1 min give or take for the runner to be ready and pick up jobs. It would be faster if the scaleUp only creates a new instance when there is none left. It means the scaleDown wil jsut shutdown the instance and not kill it so that the scaleUp will just start it up.

I am totally happy to contribute.

What do yo think?

[ScottGuymer]

This has already been raised before here https://github.com/philips-labs/terraform-aws-github-runner/issues/1166

With a long conversation about the need and issues we might run into.