Check connection status in ES administration index

Summary

This is a follow-up to !17230 (closed) / !18254 (merged) / !20421 (merged).

The ES administration currently doesn't give any indication if any of the indices aren't available.

Improvements

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:

image

Involved components

  • ee/app/assets/javascripts/elasticsearch/components/es_index_actions.vue
  • ee/lib/api/elasticsearch_indices.rb