[TSVB] Cancel discarded searches

[lukasolson]

When a user issues a search request in a TSVB visualization, we need to cancel it in the following scenarios:

1. When the user navigates away before the search completes
2. When a new search is requested before the prior one completes

[elasticmachine]

Pinging @elastic/kibana-app-arch

[Dosant]

Please note: TSVB uses search service server-side, which means they will need to listen to aborted$ event on Kibana request and then cancel underlying server-side searches

There is an example plugin that shows this: #118176

[elasticmachine]

Pinging @elastic/kibana-vis-editors @elastic/kibana-vis-editors-external (Team:VisEditors)

[Dosant]

@elastic/kibana-vis-editors, just FYI, while testing on a cluster on with a lot of data, I noticed that TSVB seem to send a request on every change in an editor. As requests are not canceled it is very easy to spam elasticsearch with long-running requests while typing into "painless script" editor and get denial of service errors

[flash1293]

Right, you can avoid this by disabling the "Auto apply" setting. We have this scheduled for 8.2