Add network_1_id and network_2_id parameters

`network_1_id` is used by the vCloud Edge Gateway gem[1]; also add `network_2_id` for later use and for consistency.

[1]:
https://github.com/alphagov/vcloud-edge_gateway/blob/8ccc1aa1617e4b2faf369a727716f0f19a76212d/spec/support/integration_helper.rb#L6

* * *

Also, fix capitalisation in the CHANGELOG.