Onnxruntime capture artifacts; dry run

[deitch]

Adds two commits.

First, adds ability to set a cache dir and a bundles dir. Each runtime can report a cache dir and, if set, will be mounted into the container. Similarly, it can report a bundles dir, which also will be mounted.

These are particularly useful for onnxruntime, where it creates a bundle from onnx, and then runs the bundle. Compiling the onnx to the bundle is by far the majority of time to get running (sometimes >90%). Those artifacts are cached in a given directory, but if it is ephemeral inside the container, it is lost. That means each run after the first takes up to ten times as long as it should be until it can start inference.

Second, for simplicity sake, adds a nekko run --dry-run option, so it can print out what it will run in docker run and then exit.