Automatic API documentation

[iblazevic]

Look into introducing automatic API documentation to skeleton. Without making it easier we are never going to write the documentation ourselves.

Since we already explicitly define all allowed body properties seems like we have the foundation to do it.

[rkatic]

A perhaps valuable option is to try to extract docs from our Joi based validations using Joi.describe(schema). Otherwise, if we opt for something like Swagger, my only concern is how to still have complex validations that we have with Joi.