feat: "Who Was Ill?" page and validation

[rhysbarrett]

JIRA link

https://companieshouse.atlassian.net/browse/LFA-1438

Change description

This commit implements the "Who Was Ill?" page, along with validation. See screenshots below.

Accessibility Note: The Conditional Input causes AXE to throw a critical accessibility error. This is a known and accepted issue within the GOV.UK Frontend system.

Work checklist

• Tests added where applicable
• UI changes look good on mobile
• UI changes meet accessibility criteria

Merge instructions

We are committed to keeping commit history clean, consistent and linear. To acheive this commit should be structured as follows:

<type>[optional scope]: <description>

and contain the following structural elements:

• fix: a commit that patches a bug in your codebase (this correlates with PATCH in semantic versioning),
• feat: a commit that introduces a new feature to the codebase (this correlates with MINOR in semantic versioning),
• BREAKING CHANGE: a commit that has a footer BREAKING CHANGE: introduces a breaking API change (correlating with MAJOR in semantic versioning). A BREAKING CHANGE can be part of commits of any type,
• types other than fix: and feat: are allowed, for example build:, chore:, ci:, docs:, style:, refactor:, perf:, test:, and others,
• footers other than BREAKING CHANGE: <description> may be provided.