Use Redis as Celery results backend.

[gibber9809]

Description

Add redis to the clp package. Once other changes are ready redis will be swapped for rabbitmq rpc for our celery results backend.

Validation performed

• verified that redis starts and stops as expected with package scripts
• verified that search queries execute as expected with the package

[kirkrodrigues]

Minor comments.

Technically, we should use a conceptual component name to avoid having it change if we switched out the underlying implementation; but since we plan to switch away from Celery, using redis as the component name seems fine.

[kirkrodrigues]

Commit message: `Use Redis as Celery results backend. (#227)'?