Draft: Add Dockerfile for Foxy

Description

Add an updated Dockerfile for ROS2 Foxy. This uses multistage building and buildkit features for caching the entire build process, while reducing the number of hard coded options and packages.

Related: #599 (closed)

Notes for Reviewer

Ubuntu Focal includes newer packages that have deprecated several aspects in the previous build.

Checklist

• Build Completes
• Update Docs
• Simplify previous entrypoint