Harmony 1996: Add 'empty-result' status to WorkItem class and work-items table

[indiejames]

Jira Issue ID

HARMONY-1996

Description

This PR adds a new status to WorkItem to represent when a service processed the work-item, but produced to data. This is to allow us to provide a better experience for users by not staging empty files.

Local Test Steps

1. Use dbViz to update a work-item's status to 'empty-result' and verify that this is allowed. (This change will not be visible anywhere until further tickets are worked)
2. Run a Harmony request and verify that it goes through okay.
3. Check the status page and workflow UI to make sure the behavior has not changed

PR Acceptance Checklist

• Acceptance criteria met
• Tests added/updated (if needed) and passing
• Documentation updated (if needed)
• [ x] Harmony in a Box tested? (if changes made to microservices)