Sb advanced fastapi gen

[sboagibm]

What this PR does / why we need it:
Improve prediction endpoint Swagger/OpenAPI generation such that (this is a checklist of intentions):

• defaults dataclass-style are observed (via "dataclass_fields_stashed")
• model_id defaults are observed via model_id_default @task
• Control over whether the shown at all via model_id_show on @task
• Control on whether the task is generated via open_api_visible on @task
• Doc strings of tasks are observed
• Doc strings of data-objects are observed
• Doc("blah blah") type annotations are observed
• Hidden() type annotations are observed (or some way to hide steps)
• Pass endpoint context, especially so accept can be observed by the task implementation
• Use non-flattened schemas
• Show output schema, when in non-zip output mode

Special notes for your reviewer:

If applicable:

• this PR contains documentation
• this PR contains unit tests
• this PR has been tested for backwards compatibility