chore(gatsby): Add getServerData to PageProps type (#34003)

Co-authored-by: Lennart <[email protected]>

Author: ashhitch

packages/gatsby/index.d.ts

@@ -80,7 +80,8 @@ export const prefetchPathname: (path: string) => void
 export type PageProps<
   DataType = object,
   PageContextType = object,
-  LocationState = WindowLocation["state"]
+  LocationState = WindowLocation["state"],
+  ServerDataType = object
 > = {
   /** The path for this current page */
   path: string
@@ -141,6 +142,8 @@ export type PageProps<
    *   ..
    */
   pageContext: PageContextType
+  /** Data passed into the page via the [getServerData](https://www.gatsbyjs.com/docs/reference/rendering-options/server-side-rendering/) SSR function. */
+  serverData: ServerDataType
 }
 
 export interface PageRendererProps {