Include rules following a checkpoint in DAG visualization

In workflows containing a checkpoint, the DAG cannot be completely visualized.

E.g. when running the second checkpoints example from the documentation, the DAG before workflow execution looks like so (collapsing all samples into one for simplicity):

clustering -> aggregate -> all

while after running the pipeline, the DAG looks like:

intermediate -> aggregate -> all

The desired outcome would be to have all steps displayed in one graph, like so:

clustering -> intermediate -> aggregate -> all

This may not be possible before workflow execution, but after workflow execution would be useful too.

Reproduce the second checkpoints example linked in the issue and compare the DAG before and after workflow execution. Trace the DAG visualization entry point responsible for those graphs; done means the post-execution visualization includes clustering, intermediate, aggregate, and all in one graph.