v5 still used throughout react

[evwilkin]

v5 is still hard coded into many React files, most frequently in example markdown files in the cssPrefix front matter causing the CSS tables not to generate correctly at the bottom of those react docs pages, but also used within some component code such as the Th component where an old v5 screen reader class is applied, causing the screen reader text content to be visible on the page:

https://github.com/patternfly/patternfly-react/blob/v6/packages/react-table/src/components/Table/Th.tsx#L233