StreamingDataSourceBuilder and filtering keys and segments

[js-commit]

Is your feature request related to a problem? Please describe.
Can you please provide an example on how to use the StreamingDataSourceBuilder filter? I've tried passing in a single flag ID, and I've noticed that the filtering does not work. Perhaps there is some syntax in how you properly use it, and it's not clear in any of the documentation.

Describe the solution you'd like

• An example on how to properly use the filter query parameter.

Additional context
The idea behind using a filter is to ensure that the service only listens to changes that it really cares about and resource usage when there are many flags.