Configuration contentTypes validation need detailed shape

[bernardodiasc]

Currently the contentTypes validation are limited to an array of object. It should define better the object shape.

Actual

contentTypes: Joi.array().min(1).items(Joi.object()).required(),

Expected

Example:

contentTypes: Joi.array().min(1).items(
  Joi.object({
    arg: Joi.string().required(),
    value: Joi.func().required(),
  })
).required(),

The problem with the snippet above is that is not valid for the need, using it just as pseudo-code.