docs: add class for header wrapper + keywords for payment guide (#12414)

www/packages/docs-ui/src/components/Heading/H1/index.tsx

@@ -9,7 +9,7 @@ export type H1Props = React.HTMLAttributes<HTMLHeadingElement> & {
 
 export const H1 = ({ className, hideLlmDropdown, ...props }: H1Props) => {
   return (
-    <div className="flex items-start justify-between gap-2">
+    <div className="flex items-start justify-between gap-2 h1-wrapper">
       <h1
         className={clsx(
           "h1-docs [&_code]:!h1-docs [&_code]:!font-mono mb-docs_1 text-medusa-fg-base",