This adds a Dockerfile and a new bash script that makes it
east to invoke the appopriate Docker commands.
This does not yet enable a GitHub Action because of intermittent
issues that we have not yet ironed out.
This adds `AutomationEngine` to libs/viewer, which iterates through
`Settings` instances that were generated from a JSON spec and applies
them to a Filament `View`. It can be configured to sleep between tests
using a time delay or a frame count.
This also adds command line arguments and user-interface elements to
`gltf_viewer` for automated testing.