feat: add support for optgroups in SelectWidget and related documentation updates#5000

nlemoine wants to merge 2 commits into

rjsf-team:mainrjsf-team/react-jsonschema-form:mainfrom

nlemoine:feat/optgroup-select-widgetnlemoine/react-jsonschema-form:feat/optgroup-select-widgetCopy head branch name to clipboard