devfile library should be able to parse version specified in parent reference

[yangcao77]

Which area this feature is related to?

/area library

Which functionality do you think we should add?

Why is this needed? Is your feature request related to a problem?
sub issue for #735

Detailed description:
Devfile Library change required for multi-version stacks/sample support. Devfile library should be able to parse version specified in parent reference.

Describe the solution you'd like

parse the new property version under parent, and call corresponding registry /v2/index endpoint to get the parent devfile content.
tests should be implemented to cover the new use case.

Describe alternatives you've considered

Additional context