[Doc] Deprecate mui v6 system props

[smeng9]

Problem

MUI System props now need to be put under sx field. https://mui.com/material-ui/migration/migrating-from-deprecated-apis/#system-props

This is not a breaking change as mui v5 also supports putting system props in the sx field instead of the props directly https://v5.mui.com/system/properties/#legend

Solution

We need to use latest guideline in mui v6 without introducing breaking change for users still using mui v5.

Also suggest to apply the codemod through jscodeshift for the packages folder https://next.mui.com/material-ui/migration/migrating-from-deprecated-apis/#system-props

How To Test

Describe the steps required to test the changes

Additional Checks

• The PR targets master for a bugfix, or next for a feature
• The PR includes unit tests (if not possible, describe why)
• The PR includes one or several stories (if not possible, describe why)
• The documentation is up to date

Also, please make sure to read the contributing guidelines.

[djhi]

Thanks!

[fzaninotto]

Thanks a lot!