fix(gatsby): don't remove onPluginInit in graphql-engine (#34558)

(cherry picked from commit 135e080)

Author: pieh

packages/gatsby/src/schema/graphql-engine/webpack-remove-apis-loader.ts

@@ -3,6 +3,9 @@ import { GatsbyNodeAPI } from "../../redux/types"
 import * as nodeApis from "../../utils/api-node-docs"
 import { schemaCustomizationAPIs } from "./print-plugins"
 
+const apisToKeep = new Set(schemaCustomizationAPIs)
+apisToKeep.add(`onPluginInit`)
+
 module.exports = function loader(source: string): string | null | undefined {
   const result = transformSync(source, {
     babelrc: false,
@@ -12,7 +15,7 @@ module.exports = function loader(source: string): string | null | undefined {
         require.resolve(`../../utils/babel/babel-plugin-remove-api`),
         {
           apis: (Object.keys(nodeApis) as Array<GatsbyNodeAPI>).filter(
-            api => !schemaCustomizationAPIs.has(api)
+            api => !apisToKeep.has(api)
           ),
         },
       ],