Defaults v2 summary title when not supplied

[jbarnsley10]

Proposed change

Default the summary title of a v2 form to 'Check your answers before sending your form' if no title is supplied (i.e. empty string). If a title is supplied, use that instead.

v1 forms cannot have an empty string as the title, so we can only use the title provided.

Another PR for forms-manager will be required to do a DB migration to do the following:

• leave V1 forms unchanged
• set any v2 forms that have summary title as 'Summary' to have summary title as empty string
• do the above for both live and draft forms

Jira ticket: DF-564

Type of change

• Bug fix
• New feature
• Breaking change
• Misc. (documentation, build updates, etc)

Checklist

• You have executed this code locally and it performs as expected.
• You have added tests to verify your code works.
• You have added code comments and JSDoc, where appropriate.
• There is no commented-out code.
• You have added developer docs in README.md and docs/* (where appropriate, e.g. new features).
• The tests are passing (npm run test).
• The linting checks are passing (npm run lint).
• The code has been formatted (npm run format).

[sonarqubecloud]

Quality Gate passed

Issues
0 New issues
0 Accepted issues

Measures
0 Security Hotspots
100.0% Coverage on New Code
0.0% Duplication on New Code

See analysis details on SonarQube Cloud

[alexluckett]

Probably not neccessary to do a check specifically on V2 to be honest, I don't think it'd ever occur as a scenario. All good anyway.