Pipeline visualization needs to depict tunable parameters

[brimoor]

Currently, visualizing a pipeline via, for example:

eta pipelines --diagram visualize_labels

will render all of the parameters for each module.

However, the pipeline may not expose all of these parameters as tunable. It would be nice if the visualizer:
(a) only rendered the tunable parameters, or
(b) added some extensions to only the tunable parameters to indicate that they are tunable

[brimoor]