Stream lookup

## What?

As a Graylog user I would like to have a stream lookup to help enrich values from another local stream.

## Why?

This would help us immensely for example if we had Stream A which is local store a mac ID and compare it to the value of Stream B which is remote. This field can be IP address, agent id (if app was reinstalled), or any field really. Since this information is "live" this cannot be accomplished with simple lookup tables. Since employees come and go constantly, this would be a helpful tool. Would this be similar in functionality to the HTTP Jsonpath or is this something else all together?

[This](https://github.com/billmurrin/graylog-plugin-slookup-function) old plugin (which is no longer maintained) is a great example.

Please see HS-560796954 for additional context and examples.