Move deduplication pillow from xform to case processor

[mjriley]

Technical Summary

Deduplication processing was triggered through the xform pillow. Unfortunately, this creates race condition headaches, as detecting duplicates relies on inspecting the elasticsearch case index -- and that index is only updated by the case pillow. Moving the logic avoids this headache.

Associated ticket: https://dimagi-dev.atlassian.net/browse/SAAS-15054

Safety Assurance

Safety story

I've run the case processor locally to ensure that the deduplication processor is picking up case submissions.

Automated test coverage

A few new tests suites were added or expanded to verify that we can filter case changes to only a specific affected case.

QA Plan

No QA planned.

Rollback instructions

• This PR can be reverted after deploy with no further considerations

Labels & Review

• Risk label is set correctly
• The set of people pinged as reviewers is appropriate for the level of risk of the change