Add resources for address groups and service groups

[jan-walther]

This PR adds support for address_groups and service_groups as outlined in #170.

This PR also adds preliminary data sources for address_groups.

resource "nutanix_service_group" "test_service" {
  name = "test-2"
  description = "test"

  service_list {
      protocol = "TCP"
      tcp_port_range_list {
        start_port = 22
        end_port = 22
      }
      tcp_port_range_list {
        start_port = 2222
        end_port = 2222
      }
  }
}

resource "nutanix_address_group" "test_address" {
  name = "test"
  description = "test"

  ip_address_block_list {
    ip = "10.0.0.0"
    prefix_length = 24
  }
}

[abhimutant]

PR needs some changes that we are done with. We will merge it in new branch and cherry-pick the new changes and the test cases we added.