82557: Add all the logic to handle DB insertion with uploads controller

[balexandr]

In support of sending an email update to a VFMP applicant, the PEGA response that represents the applicants data needs to be stored in the VA.gov back end.

This is Part A of this ticket as it handles the initial DB insertion and setup for part B

Summary

• Update database to remove email uniqueness index; Add index for form_uuid
• Update model to remove validation
• Update existing models to include email and uuid
• Add DB creation when file is being uploaded
• Add Rspec to ensure database record is being added
• Update existing tests

Related issue(s)

• Map PEGA responses to vets-api back end va.gov-team#82557

Screenshots

Testing done

• Rspec tests
• Manual tests

Acceptance criteria

Given a well-formed call to the callback endpoint
When the response is received
Then the response should be persisted so that status can be send back to the applicantexpected