fix: Allow formData to be optional everywhere

[heath-freenome]

Reasons for making this change

Fixes #3305 by ensuring that formData can be optional everywhere

There were some types which were requiring formData to be required even though it really can be optional everywhere

• In @rjsf/utils, updated the formData prop in all types where it was required to make it optional
  • Also updated all function arguments where it was required to make formData optional
• In @rjsf/validator-ajv6 and @rjsf/validator-ajv8, updated places where formData was required as a function parameter to make it optional instead
• In @rjsf/core, updated places where formData was required as a function parameter to make it optional instead
• In utility-functions.md, updated the documentation of optional parameters without default values to ensure they included | undefined in the type of the parameter
• In 5.x upgrade guide.md, updated the note about improved typescript typing in @rjsf/utils to indicate that it may require updating typing in the user's implementations
• Updated the CHANGELOG.md accordingly

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 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