Grafana-UI: add storysource addon to Storybook (#22490)

* Add @storybook/addon-storysource

* Enable the addon

* Fix Select label

* Lock storysource version

packages/grafana-ui/.storybook/main.ts

@@ -5,5 +5,6 @@ module.exports = {
     '@storybook/addon-actions',
     '@storybook/addon-docs',
     'storybook-dark-mode/register',
+    '@storybook/addon-storysource',
   ],
 };