abstract reporting file storage as duplex stream

[ppisljar]

Reporting stores generated reports in elasticsearch (pdf, csv, png). In order to abstract that away and allow us to implement new storage locations in the future we will implement the current store as a duplex stream. This should make it much easier to consume as well as easier to support different streams in the future (like simple filesystem steam).

const stream = createWritableEsStream(id);
stream.write(myRawData);
stream.end();

const stream = createReadableEsStream(id);
for await (chunk in stream) {
  console.log(chunk);
}
stream.close();

[elasticmachine]

Pinging @elastic/kibana-reporting-services (Team:Reporting Services)

[elasticmachine]

Pinging @elastic/kibana-app-services (Team:AppServices)