Add support for "--concurrency".

[ShaheedHaque]

As of #3, and as per celery/celery#7874 (comment), the code is missing support for --concurrency. I know we have not had the assistance/input/review we would have liked on the basic design, but I propose that we try to progress with support for multiple processes. Thoughts?

[Andrew-Chen-Wang]

Note: anyio integration for celery is planned by the celery team. Not sure if that will complicate multiprocessing support.

[ShaheedHaque]

Note: anyio integration for celery is planned by the celery team. Not sure if that will complicate multiprocessing support.

@Andrew-Chen-Wang interesting...do you have a link to that?

[Andrew-Chen-Wang]

Sorry, I should rephrase: if the team decided to implement asyncio, they would "probably" use anyio:

celery/celery#6483 (comment)

[auvipy]

No that will not complicate multiprocessing support. bcz making multiprocessing async compatible is also a target