Fixed optional data controls images in docs

[heath-freenome]

Reasons for making this change

Fixed the syntax for the optional data controls to use the proper Markdown syntax per their docs

right now they are broken, see the docs

Checklist

• I'm updating documentation
  • I've checked the rendering of the Markdown text I've added
• I'm adding or updating code
  • I've added and/or updated tests. I've run npx nx run-many --target=build --exclude=@rjsf/docs && npm run test:update to update snapshots, if needed.
  • I've updated docs if needed
  • I've updated the changelog with a description of the PR
• I'm adding a new feature
  • I've updated the playground with an example use of the feature

Before:

After: