Add support for meta information

[rightisleft]

Description

• What is the motivation / use case for changing the behavior?

This library should be interoperable with data produced from custom states:

Example here: https://www.distributedpython.com/2018/09/28/celery-task-states/

Given that Worker A needs to consume custom meta information produced by Worker B
When Worker A is looking at a Result
Then there should be a method that exposes an object such a { state: string, meta: any}

• Proposed Behavior
  add Result.statusState(): { state: string, meta: any} { ... }

• Other information (e.g. detailed explanation, stacktraces, related issues, suggestions how to fix, links for us to have context, eg. stackoverflow, gitter, etc)

Writing custom states would need to conform to the expected interface in the python library and is likely out of scope for this request.

[rightisleft]

Starting:
https://github.com/rightisleft/celery.node/tree/feature/custom-states