[FEA] Tool to visualize the architecture/inspect the architecture

[bschifferer]

🚀 Feature request

As a user, I want to visualize the architecture and way to debug/understand the architecture.

NVTabular + Merlin Models are a powerful tool to provide easy ways to define/train a model. However, it is a "black box" and it is easy to make mistakes in the model design (e.g. target column is tagged for an input). As a user, I want a simple way to visualize the architecture.