Ce/connect messaging

[calellowitz]

Product Description

This adds connect messaging as a new message type in the messaging framework. It does not currently support form sessions although I will add those prior to merge. That said, I wanted to open this up to review now since it is quite large and touches a fair amount of complex code.

Technical Summary

Tech Spec: https://docs.google.com/document/d/1FgsXr0PLR7Btq2fOBeXIMs_OziBRsUsATgHgWna0h5M/edit?tab=t.0#heading=h.3rzu21agk2m3
Design Doc: https://docs.google.com/document/d/1h3bcZ4oQAnOu5aGW8Rue0TnbiaW2OXWMaqNKwI6RciE/edit?tab=t.0#heading=h.ipgou4bu0qoj

The linked docs provide much of the context

Feature Flag

COMMCARE_CONNECT for now, but I expect to migrate it to its own flag so that it can be enabled independently of the rest of the connect features.

Safety Assurance

Safety story

Existing messaging paths have automated coverage, and are only minimally modified. The new code is almost entirely self contained and will go through a QA process.

Automated test coverage

QA Plan

No QA ticket yet since it is not finished, but I will add it once it starts.

Migrations

• The migrations in this code can be safely applied first independently of the code

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