Add ``project_id`` to response body of list group snapshots
with detail and show group snapshot detail APIs.
Merging the group and group snapshot response in same MV
was discussed in weekly meeting[1].
[1] http://eavesdrop.openstack.org/meetings/cinder/2019/cinder.2019-02-20-16.00.log.html#l-122
Change-Id: Ided66450b5d7de32551edbce249e94f6174da2eb
Implements: blueprint add-project-id-to-group-groupsnapshot-response