[JS] Allow an event to be redirected to another stream

Phuedxrequested to merge
work/phuedx/T401380-2 into main

What?

If the config for stream S1 has the producers.metrics_platform_client.stream_name property that refers to another stream S2 and S2 is configured, then check that S1 is in-sample and, if so, submit the event to S2.

Why?

xLab UI allows analytics instrument owners to specify a target stream. The target stream may be product_metrics.web_base or it may be something else.

In all other ways, instruments and streams are configured the same way and therefore can be modelled using the StreamConfig type. However, submit() needs to be tweaked slightly to handle the difference in behavior transparently.

Bug: T401380

Edited by Phuedx

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