Make association two-way

[kayline]

Summary

• This work is behind a feature toggle (flipper): NO - model existence is not behind a flipper. All behavior is.
• Previously added a belongs_to to SecondaryAppealForm, needed the has_many on AppealSubmission
• optional, dependent: destroy
• Decision Reviews, yes

Related issue(s)

department-of-veterans-affairs/va.gov-team#95001

Testing done

• New code is covered by unit tests
• Could find the AppealSubmission from the SecondaryAppealForm, but not the other way
• Create an AppealSubmission with SecondaryAppealForm in staging, verify in console that lookup works both ways

Screenshots

Note: Optional

What areas of the site does it impact?

No user facing changes, just a Rails association

Acceptance criteria

• I fixed|updated|added unit tests and integration tests for each feature (if applicable).
• No error nor warning in the console.
• Events are being sent to the appropriate logging solution
• Documentation has been updated (link to documentation)
• No sensitive information (i.e. PII/credentials/internal URLs/etc.) is captured in logging, hardcoded, or specs
• Feature/bug has a monitor built into Datadog (if applicable)
• If app impacted requires authentication, did you login to a local build and verify all authenticated routes work as expected
• I added a screenshot of the developed feature

[shaunburdick]

LGTMMTGL

[github-actions]

Backend-review-group approval confirmed.