RP 12.7, parent-child pipelines - correction to show available in Core

Why is this change being made?

Correction to show parent-child pipeline feature is available for Core; which will also sync up with what is already correctly indicated on the feature.yml file.

Does this MR meet the acceptance criteria?

Conformity

• Added description to this MR explaining the reasons for the proposed change, per say-why-not-just-what