Truncate long fields in Discover server-side

[timroes]

Currenty Discover loads all fields not filtered via the index pattern field filters. This can become problematic if some fields contain very large data that users are not (yet) aware of, thus they might not have had a chance to filter it out via the index patter field filters. Also there might be the case where just some documents contain really large field values. I think we should try to get to a way where we by default will have Elasticsearch truncate long values for us by default (at a reasonably high length) and then show the truncated value and only load the full value of a field once the user explicitly states she wants (i.e. we have "view full field" besides those truncated values).

This would save potentially a lot of bandwidth for documents containing longer values and much more important, makes Kibana faster, since even when not showing those values (i.e. we would truncate them client side) we still need to parse the response and do some level of postprocessing/transformation in our querying highlight.

Related issues: #11457

Blocked on elastic/elasticsearch#72453

[elasticmachine]

Pinging @elastic/kibana-app (Team:KibanaApp)

[kertal]

Closing this because it's not planned to be resolved in the foreseeable future. It will be tracked in our Icebox and will be re-opened if our priorities change. Feel free to re-open if you think it should be melted sooner. We're always interested in hearing our users opinions, especially if they are Tim Roes ❤️!