generate optional properties

[Danielecina]

📄 Description

Previously json-schema-faker would randomly generate optional properties.
Now json-schema-faker generates all example properties every time

📹. Gif

✅ Checklist

• your branch will not cause merge conflict with master
• run npm test
• tests are included
• the documentation is updated or integrated accordingly with your changes
• the code will follow the lint rules and style of the project
• you are not committing extraneous files or sensible data