Copy as cURL should provide a hint about needing to be configured for Cloud

Now that the **Copy as cURL** link can be made to work for Cloud and we want to use it in our Cloud docs, it would be good to prompt users to configure it. User need to add their own Cloud endpoint URL and user name to replace the default `localhost:9200`, or it's going to fail out of the box every single time. Which makes for a poor user experience. 🙂

This is the link:


This is the config dialog where you need to add an endpoint and user name:


Ideas:

* As discussed with @Adrian-J , we don't want a modal to pop up on first use. Unwanted modals make for a poor user experience by immediately taking focus away from the page you're on.
* We do want to provide a hint that you need to configure this once when you're in the Cloud docs. E.g. you could grey out the **Copy as cURL** link with a ⚠️ triangle or add an overlay with a top that tells you to configure these option to make it all work.

This will need some design work from Adrian first before we start talking about the implementation.

@nik9000 @philkra FYI