Check connection status when editing index in ES administration

Summary

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

This also builds on the proposed changes in #38128, and possibly #38127.

Currently it's possible to update an ES index in the administration with invalid values, e.g. a URL which isn't reachable, or where the index doesn't exist.

Improvements

The same connection check that's implemented with #38128 should be performed when updating an ES index, and in case of failure a corresponding validation error should be displayed in the form, and the DB record should not be updated.

Involved components

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