opentelekomcloud_dc_virtual_interface_v2 with wrong example and mandatory value

[Bruno Forghieri Agueda]

On the examples for the opentelekomcloud_dc_virtual_interface_v2 documentation, the examples states the argument vgw_id, but it should be virtual_gateway_id

And the argument service_type is declared as optional, but it is required

[Anton Sidelnikov]

Done