fix(gatsby-recipes): add isLocal to schema for GatsbyPlugin (#28417)

Author: KyleAMathews

packages/gatsby-recipes/src/providers/gatsby/plugin.js

@@ -524,6 +524,7 @@ const schema = {
   name: Joi.string(),
   description: Joi.string().optional().allow(null).allow(``),
   options: Joi.object(),
+  isLocal: Joi.boolean(),
   readme: Joi.string().optional().allow(null).allow(``),
   shadowableFiles: Joi.array().items(Joi.string()),
   shadowedFiles: Joi.array().items(Joi.string()),