Addition of a new allotted resource "connectivity attachment" to
generic-resource-api schema. Connectivity attachment will be provided
by Connectivity service and will be allotted to Site service as part
of CCVPN use case. This new allotted-resource can serve for both
SOTNAttachment and SDWANAttachment.
Change-Id: Iff5ad46a72d55bc83ca36e4703d439e43fe948ce
Issue-ID: SDNC-384
Signed-off-by: Gaurav Agrawal <gaurav.agrawal@huawei.com>