Prettier: Add prettier config that imports prettier from toolkit (#23729)

.prettierrc.js

+module.exports = {
+  ...require('@grafana/toolkit/src/config/prettier.plugin.config.json'),
+};

package.json

@@ -57,9 +57,6 @@
       "git add"
     ]
   },
-  "prettier": {
-    "trailingComma": "es5"
-  },
   "devDependencies": {
     "@babel/core": "7.8.4",
     "@babel/plugin-proposal-nullish-coalescing-operator": "7.8.3",