Check connection status in ES administration index
The ES administration currently doesn't give any indication if any of the indices aren't available.
In the backend, we need to provide a new API endpoint to get the connection status for a given index. This should check if the ES cluster is reachable, the index exists with the configured name, and maybe even verify that the settings/mappings match the configured version.
In the frontend, this should be displayed as in the proposed designs: