Add a Redis environment variable for sidekiq

[noellabo]

Add an environment variable to configure a Redis server dedicated to Sidekiq.

• SIDEKIQ_REDIS_HOST
• SIDEKIQ_REDIS_PORT
• SIDEKIQ_REDIS_DB
• SIDEKIQ_REDIS_PASSWORD

or

• SIDEKIQ_REDIS_URL

If you want to separate Redis on a server that is already in operation, you need to migrate the key for Sidekiq to a new Redis. It includes, but is not limited to, the following keys:

dead
processes
queues
queue:*
retry
schedule
schedules
schedules_changed
sidekiq-scheduler:*
stat:*
uniquejobs:*

Alternatively, you can use the brand new Redis without migrating if you don't have to worry about past statistics or jobs being retried. Even so, it's a good idea to remove the key from your old Redis.