Add backend support for handling case mappings within Form Builder

[mjriley]

Product Description

Technical Summary

This is the HQ half of the Form Builder changes. This modifies the context we send down to Vellum so that Vellum's case management plugin has access to the current mappings and the case property suggestions.

Case property suggestions are populated by calling get_all_case_properties_for_case_type. It should be noted that this can be very slow, especially on large domains. It is currently the same call used within the data cleaning tool and the case management page, but because the use case of form builder is different, the slowness with this call is more severe here and likely requires a followup improvement. For these reasons, I'm considering this a "High Risk" PR until this changes (and would not suggest releasing it as is).

Feature Flag

saas_formbuilder_save_to_case

Safety Assurance

Safety story

Tested locally, on staging, and run through QA.

Automated test coverage

Various test suites added

QA Plan

Currently running through QA

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