Add "next" job field to swagger

[FedeBev]

Is your feature request related to a problem? Please describe.
Add next filed to job model in swagger definition.

Describe the solution you'd like
Simply add the next field to the job definition, it should work out of the box if I'm not mistaken

definitions:
    job:
        .....
        next:
            type: string
            format: date-time
            readOnly: true
            description: "Time of the next job execution"

Additional context
For my application I generate the client from the swagger definition, and my use case requires to known when the next job execution will be. At the moment I have to patch the swagger file manually and it's a bit annoing