add optional property version for parent reference to support multi-version stacks/samples

[yangcao77]

Which area this feature is related to?

/area api

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 Spec change required for multi-version stacks/sample support.

Describe the solution you'd like

Add optional property version for parent reference to support multi-version stacks/samples.
Create validation on the version property:

• The version should be either with a common version pattern, or be latest.
• version should only be used when id is specified. (Pull from registry)

Describe alternatives you've considered

Additional context

[yangcao77]

For the case putting version= latest, the devfile schema version might be incompatible if a newer stack version released, since latest always point to the newest version.
e.g. main devfile is devfile v2.1, and latest stack version contains devfile with v2.2

3 alternatives:

1. continue use latest stack version, and error out if the parent version is higher than the main devfile version (already included in current devfile validation)

2. use main devfile version as maxSchemaVersion, and only find the latest stack version which is small or equal than the maxSchemaVersion (main devfile version)

3. introduce minSchemaVersion and maxSchemaVersion properties in the parent's import reference as well. and apply the two filters when looking for "latest" stack version.

I personally prefer the first/second option. 3 is complicated from devfile writer perspective

[elsony]

Discussed on the community call on 3/7 and we'll use option #1.