Introduce generic error response schema

[bglamadrid]

When the application implementing this API is unable to fulfill any request as usual, the resulting response from said application should be formatted in an orderly manner.

For this, the following tasks should be done:

• Create a schema named AppError and have it contain these properties
  • code: string
  • message: string
  • detailMessage: string
  • canRetry: boolean
• Create a response schema using the former
• Link this response in every error case; for status codes 400, 403, 404 and 500

This WILL break API compatibility, since there was no defined behavior prior to this; each application could format these responses and/or expect to be formatted differently from each other.