[SD-1484] get multistep validation working as expected

[lambry]

Issue: https://digital-vic.atlassian.net/browse/SD-1484

What I did

• Get multistep validation working as expected and reinstate related test. The before-step-change hook used to run before the steps validation, now it runs after, we do our own thing for validation anyway so we can 'disable' their step validation.

How to test

• https://app.pr-292.reference-sdp-vic-gov-au.sdp4.sdp.vic.gov.au/test-wf

Checklist

For all PR's

• I've added relevant changes to the project Readme if needed
• I've updated the documentation site as needed
• I have added tests to cover my changes (if not applicable, please state why in a comment)

For new UI components only

• I have added a storybook story covering all variants
• I have checked a11y tab in storybook passes
• I have added cypress component tests (if the component is interactive)
• Any events are emitted on the event bus using emitRplEvent