Support multiple machine types

[nguyenhoaibao]

As title, can we support creation of multiple machine types, by using GH Actions runs-on label?

For example, a job in a workflow selects:

runs-on: [self-hosted, n2-standard-4]

then the script does:

1. Check if the machine type is valid, and
2. If it's valid, create a runner with that machine type.
3. If it isn't, use default machine type.