✨ Extend the code generator for JobItems

[aorabdel]

Description

This change refactors the generator to be able to handle multiple types of generation, and extends it with a new type for JobItems, which are schemas that have the property x-job: true.

The code generated for the the JobItems implements missing methods that would make these JobItem types satisfy the IAsynchronousJob interface defined here.

• This change is covered by existing or additional automated tests.
• Manual testing has been performed (and evidence provided) as automated testing was not feasible.
• Additional tests are not required for this change (e.g. documentation update).