Add Postman Collection

[vladyslav-fenchak]

Leave a PostMan collection in the root of the project.
This way, anyone who wants to test this project, only needs to start the services and import the collection to PostMan, having already the example requests and everything configured.

[vladyslav-fenchak]

@Clariteia/core-devs what do you think about having this?
If not here, we could have it uploaded somewhere else, but I think it would be nice to have everything we need within this example project.

[albamig]

To me it is certainly worth having that as an extra, so anybody with PostMan skills can take a quicker look at our API.