plugins/graphiql: initial migration to new system

Co-authored-by: Camila Belo <camilaibs@gmail.com>
Co-authored-by: Johan Haals <johan.haals@gmail.com>
Co-authored-by: Philipp Hugenroth <philipph@spotify.com>
Signed-off-by: Patrik Oldsberg <poldsberg@gmail.com>

plugins/graphiql/src/alpha.tsx

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+/*
+ * Copyright 2023 The Backstage Authors
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+import React from 'react';
+import {
+  createPageExtension,
+  createPlugin,
+} from '@backstage/frontend-plugin-api';
+
+/**
+ * @alpha
+ */
+export const GraphiqlPage = createPageExtension({
+  id: 'graphiql.page',
+  defaultPath: '/graphiql',
+  component: () => import('./components').then(m => <m.GraphiQLPage />),
+});
+
+/**
+ * @alpha
+ */
+export const graphiqlPlugin = createPlugin({
+  id: 'graphiql',
+  extensions: [GraphiqlPage],
+});