feat(v2): blog + docs multi-instance plugins (#3204)

* stable createData namespacing + second-blog dogfooding

* Docs: support multi-instance + make community docs a separate instance

* tests: add 2nd docs instance to versioned site

* fix docs version cli tests

* fix docs versioning cli

* typo

* team: add link to my site

* better extendCli integration

* fix metadata tests

* tests for versioned site with second docs instance

* move some validation code to utils-validation

* fix missing dependency

* fix bad compiled output due to importing constants in ./client folder

* make docs tests easier to maintain

* refactors

* prevent lodash imports in client bundle

* redirect old community docs to new urls

packages/docusaurus-utils-validation/src/validationSchemas.ts

@@ -0,0 +1,27 @@
+/**
+ * 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.
+ */
+import * as Joi from '@hapi/joi';
+
+export const PluginIdSchema = Joi.string()
+  .regex(/^[a-zA-Z_\-]+$/)
+  // duplicate core constant, otherwise cyclic dependency is created :(
+  .default('default');
+
+const MarkdownPluginsSchema = Joi.array()
+  .items(
+    Joi.array()
+      // TODO, this allows [config,fn] too?
+      .items(Joi.function().required(), Joi.object().required())
+      .length(2),
+    Joi.function(),
+  )
+  .default([]);
+
+export const RemarkPluginsSchema = MarkdownPluginsSchema;
+export const RehypePluginsSchema = MarkdownPluginsSchema;
+
+export const AdmonitionsSchema = Joi.object().default({});