Add KGX release version used

[colleenXu]

To address #568 based on decisions in today's TRAPI meeting.

TBD discussion needed first:

• Value: link to KGX storage versioned graph-metadata file (example) or the release-version only? Assigned to @tokebe to ask Adil if there's any issue using the link
• Field name: could be more general like data_version? But maybe depends on what value is (keep specific if value is version only - needs more descriptive, make general if value is link).

[tokebe]

I would argue we want a generic field name and allow a string value, so non translator-kg resources are still fine.

[tokebe]

From discussion: change field to data_release_version and make the type an object with values of str, minimum properties 1, with the overall field not required (matching the other version fields)

[colleenXu]

Looks like the spec/example is fine in swagger editor