[Docs Site] Support legacy q param in search (#20812)

Author: KianNH

src/components/search/InstantSearch.tsx

@@ -15,7 +15,7 @@ function SearchBox(props: UseSearchBoxProps) {
 
 	useEffect(() => {
 		const params = new URLSearchParams(window.location.search);
-		const query = params.get("query");
+		const query = params.get("q") ?? params.get("query");
 
 		if (query) {
 			refine(query);