Add Distributed Firewall button to vCloud menu

With v8.20 of vCloud Director and NSX 6.3, VMware added the ability for tenants to self-manage their distributed firewall through the vCD Tenant Portal.  Having a button under vCloud that acted similarly to the "Services" button for advanced edge gateways would give our tenants the ability to manage their DFW without needing to login to vCD.

URL would follow this convention: https://{vcloud director url}/tenant/dfw