Http Service should provide ability to proxy incoming requests

[mshustov]

Kibana provides own abstraction on top of the HTTP server, so dealing with KibanaRequest and KibanaResponse is not always makes sense because they were created to hide low-level details.
We already had a problem implementing #36907 when we needed access to all request headers. It looks like Http Service should support proxying requests out of the box, without exposing all request details.
Server should support request streaming to reduce memory footprint. Usage in Legacy: 1 2

Note: Legacy platform provides hapi h2o2 plugin to the plugins, but it doesn't mean we should do so.

[elasticmachine]

Pinging @elastic/kibana-platform

[joshdover]

Note that the proxy endpoint in the Elasticsearch plugin is going away, but the Console one will still need to be supported.

[joshdover]

It appears the proxy route in console does not require anything special other than support for streaming responses. I believe this may be possible after #50783 is merged. @afharo can you confirm?

[afharo]

Exactly, after #50783 is merged, we'll be able to support stream responses and larger payloads if required.

[afharo]

Also parse: false | 'gunzip' from the examples in the description.

[joshdover]

Great, can you make that PR close this issue as well?

[afharo]

done!

[afharo]

Closing as #50783 has been merged (for some reason it didn't close automatically)

[mshustov]

Reopened. Plugins proxying requests to elasticsearch will start failing when we merge #55670
related discussion https://github.com/elastic/kibana/pull/55690/files/5f76f38499821841a478d7fe9887f31090e14d85#r371806086