[DataDiscovery] Turn off bsearch in Serverless

[thomasneirynck]

Describe the feature:

Turn off the use of bsearch in Serverless for Dashboards. Retain default behavior for Cloud and Stateful.

Turning off this should also include minimize the work on kibana server, by eliminating the custom base64 encoding logic.

The data should remain compressed. Consider default gzip-compression. Consider having Elasticsearch compress the response (https://www.elastic.co/guide/en/elasticsearch/client/javascript-api/current/basic-config.html) and just streaming back the data.

Describe a specific use case for the feature:

The proxy already supports a http2 connection, so the browser->proxy connection does not need the bsearch work-around.

This would be a good test run to validate a few key assumptions:

• browser will use http2 multiplexing to avoid default browser connection limit
• base64n compression overhead can be eliminated, eliminating the majority of work on kibana server.

proxy->kibana-server connection would remain http1. The assumption is that the overhead of multiple http-handshakes on kibana-server is minimal compared to the overhead of compression and client-side batching.

[elasticmachine]

Pinging @elastic/kibana-data-discovery (Team:DataDiscovery)