IP Space integration - Githubissues

This PR finalizes IP Space integration to the SDK which was started in #578.

It now adds support for the integration layer which consists of:

Additional field for external network to support IP spaces
IP Space Uplink management for external networks with new type IpSpaceUplink
IP Space IP and Prefix Allocation using new type IpSpaceIpAllocation
IP Space Org allocation to define custom quotas using new type IpSpaceOrgAssignment

Additionally, a type TaskResult is attached to Task as IP Allocation Requests return values in that field.

Tested on 10.3.0 (validated test skips), 10.4.1, 10.4.2

vmware / go-vcloud-director