update: use separate worker service for each queue

[nathanfranklin]

Overview:

This PR changes the local dev docker compose so that we have a single worker service for each queue. So now instead of one worker service running celery twice, we have a service for the heavy queue and a service for the default queue.

In #220, we added a heavy queue. Two comments at the time were about

• how the celery tasks was running twice and not in foreground in the worker service Task/WG-383: add queue for heavy tasks #220 (comment)
• how we couldn't see in the logs the queue being run on: Task/WG-383: add queue for heavy tasks #220 (comment)

Testing Steps:

1. Confirm you can load an image (default queue) and import a point cloud (heavy queue)

[rstijerina]

Cool! New syntax we're using, should we link to documentation in a comment?
https://docs.docker.com/reference/compose-file/fragments/