Accessibility improvements on newly added features

[TheDancingClown]

📝 A short description of the changes

• Deactivate assessors feature - the radio button label is clickable however it is not obvious to the user so hover styles are added to increase the clickable target.
• Adds more descriptions to error messages on matrix and by_year questions
• Adds aria attributes to file uploads

🔗 Link to the relevant story (or stories)

• https://app.asana.com/0/1200504523179345/1207135606763709

Deployment implications

• None

✅ Checklist

• Features that cannot go live are behind a feature flag/env var or specify deploy date and open PR as draft
• I have checked that commit messages make sense and explain the reasoning for each change
• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have made corresponding changes to the documentation
• I have added tests that prove my fix is effective or that my feature works
• I have squashed any unnecessary or part-finished commits