feat(v2): add themeConfig validation to algolia theme (#3133)

* Algolia theme option validation

* validateThemeConfig

* remove useless runtime check

packages/docusaurus-theme-search-algolia/src/validateThemeConfig.js

@@ -0,0 +1,34 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+const Joi = require('@hapi/joi');
+
+const DEFAULT_CONFIG = {
+  // By default, all Docusaurus sites are using the same AppId
+  // This has been designed on purpose with Algolia.
+  appId: 'BH4D9OD16A',
+};
+exports.DEFAULT_CONFIG = DEFAULT_CONFIG;
+
+const Schema = Joi.object({
+  algolia: Joi.object({
+    appId: Joi.string().default(DEFAULT_CONFIG.appId),
+    apiKey: Joi.string().required(),
+    indexName: Joi.string().required(),
+  })
+    .label('themeConfig.algolia')
+    .required()
+    .unknown(), // DocSearch 3 is still alpha: don't validate the rest for now
+});
+exports.Schema = Schema;
+
+exports.validateThemeConfig = function validateThemeConfig({
+  validate,
+  themeConfig,
+}) {
+  return validate(Schema, themeConfig);
+};