feat(gatsby): Refine typing on createPages’ graphql function (#14575)

* Refine typing on createPages’ graphql function

* Further refinement to createPages’ GraphQL fn to accept variables generic

Author: ryanditjia

packages/gatsby/index.d.ts

@@ -600,7 +600,13 @@ export interface PluginOptions {
 export type PluginCallback = (err: Error | null, result?: any) => void
 
 export interface CreatePagesArgs extends ParentSpanPluginArgs {
-  graphql: Function
+  graphql<TData, TVariables = any>(
+    query: string,
+    variables?: TVariables
+  ): Promise<{
+    errors?: any
+    data?: TData
+  }>
   traceId: string
   waitForCascadingActions: boolean
 }