Continue with Networks API

Let's continue with the Networks. The API is described [here](https://docs.docker.com/engine/api/v1.37/#tag/Network). 

See [contributing guidelines](https://github.com/amihaiemil/docker-java-api/blob/master/CONTRIBUTING.md). Also, [this](https://www.yegor256.com/2014/04/15/github-guidelines.html) might be helpful.