[FEATURE] Add support for networks

[RadovanTomik]

Brief description.
Add support for networks.

Desired functionality acceptance criteria
Has the following attributes:

• URI/That resolves to a link
• Name
• External id
• Contact email
• Set<Person> managers
• Set<Organization> members;

[erfannvb]

Hello @RadovanTomik. I was checking the project and I kind of liked it. I am a new Spring Boot developer. I'd be glad if I could help with contributing to this project.

[RadovanTomik]

Hi, sure all contributions are appreciated. Feel free to fork the project, pick an issue and open a PR.