Descriptions for Test Steps and Test Plans

Add a description property.

changed milestone to %9.13

added Feature flow::Merge Requested labels

mentioned in merge request !840 (merged)

closed with merge request !840 (merged)

mentioned in commit b81bdf0a

Implemented. Verified on OpenTAP 9.13.0-beta.44

added QA Verified label

mentioned in merge request !845 (merged)

mentioned in merge request !1022 (merged)