fix: Add importlib-metadata constraint to avoid celery import bug

[matthewfeickert]

Resolves #89

• Fix requires a new release of kombu
  • c.f. Celery Import Error celery/celery#7783 (comment)
• This should be viewed as temporary. As soon as there is a new release of kombu the release with this fix in in should get yanked in favor of a new release without this restriction.
• Add lower bound of celery>=5.0.0.

* Fix requires a new release of kombu
   - c.f. https://github.com/celery/celery/issues/7783#issuecomment-1283638046
   - This should be viewed as temporary. As soon as there is a new release of kombu
     the release with this fix in in should get yanked in favor of a new release
     without this restriction.
* Add lower bound of celery>=5.0.0.

[matthewfeickert]

Celery should be monitored for a new release that will remove the need for this constraint.