[POC] Add postcode/housenumber to postcode lookup entrypoint in form

[alexluckett]

Proposed change

Jira ticket:

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 failed

Failed conditions
75.0% Coverage on New Code (required ≥ 90%)

See analysis details on SonarQube Cloud

[alexluckett]

POC complete. Refined solution merged into main branch.