EL-1236: Proof of concept

[patrick-laa]

Jira ticket

What changed and why

When the user is in a change-answers loop, keep their new session data in a separate place until they complete the loop. That way if they 'back' out of it half way through the loop, their answers are still in a valid state.

Guidance to review

Checklist

Before you ask people to review this PR:

• Tests and rubocop should be passing
• Branch is generally up to date with main Github - definitely no conflicts
• No unnecessary whitespace changes. These make diffs harder to read and conflicts more likely.
• PR description says what changed and why, with a link to the JIRA story.
• Diff has been checked for unexpected changes being included.
• Commit messages say why the change was made.