Use SideKiq for email ActiveJob queues

[rladdusaw]

User story

While the default Rails queue seems to work, SideKiq would give us better visibility and potentially better reliability for jobs

Acceptance criteria

The application uses SideKiq for queues and can be deployed

• I can send emails using SideKiq
• I can track asynchronous email jobs in SideKiq
• Emails sent on the staging and qa environments are caught by mailcatcher
• Deployment does not cause emails to get lost.
• Use the catalog-indexers for sidekiq
• Run it a systemd service (ansible update)

Implementation notes, if any

The endpoint for /sidekiq will need some form of authentication to prevent unauthorized users from accessing the web frontend.

[sandbergja]

Re-opening since we reverted #4702. Emails sent from Requests are not compatible with sidekiq. We need to refactor these emails to only use data that sidekiq can handle.