Support evaluation parameters

[cathywu]

Feature Description

We have environments which permit specifying variable vehicle inflows, vehicle densities, etc. (upon reset). However, when evaluating, we may want to evaluate on a specific inflow or density. For instance, when comparing against other methods for a specific setting.

How can this be supported naturally for a variety of environments? Do we want a separate EvaluationParams object?

Environments so far which can benefit from this include:

• WaveAttenuationEnv
• DesiredVelocityEnv
• TrafficLightGridEnv

[AboudyKreidieh]

In other repositories you'd have a separate evaluation environment, which would be the same as the training environment but for a few inputs (e.g. setting a specific inflow). If this is something we're interested in, we can consider setting a flow_params input to the visualizers.

[cathywu]

I wonder if it would make sense to have option command line inputs to the rllib visualizer for this purpose? Those parameters can feed a flow_params object like you suggest.