Make Server connection status more useful

Patch proposal suggestion:

Update the Search API server connection routine to retrieve and expose Elasticsearch cluster details: cluster name, node version, and health status.
On connection failure, capture and display the HTTP response code and error message.
Modify the admin UI rendering (Controller + Twig) to conditionally display the enriched status or failure details.
Ensure all added strings are translatable and update the .pot/.po translations accordingly.

I had apparently pushed to the wrong issue fork in #2... I've now created a merge request in the correct issue fork: I apologize for the confusion.

I had been hesitating on this patch because it requires additional permissions...

1. additional cluster-level permission: monitor
2. additional index-level permissions: maintenance, monitor

That being said, when I was writing the guide on setting up an API key with a role descriptor → , I included these permissions, so it's probably okay for now.

Probably a better solution would be to test whether or not we have these permissions before trying to access data that requires it (i.e.: because we could selectively display information based on what the API key we're connecting with has permission to view). Ideally, Elasticsearch has a has-privileges API and a get application privileges API we could use to query this; another option could be to try getting the data and catching 403 errors, but the Elasticsearch Connector module doesn't yet have infrastructure to support either of those approaches.