Add ARM build and update JLink + Structurizr. +semver:minor (#31)
Changes:
- Remove Firefox (the VSCode Live Preview extension works better, Chromium is required for Markdown -> PDF conversions)
- Install Git and Git LFS through the standard Ubuntu update sites.
- Add ARM64 container build
- Enable docker build caching
- Update JLink to v7.96e
- Update Structurizr
- Install structurizr to `/opt` instead of `/usr/bin`
- A symlink to `/usr/bin/structurizr/structurizr` is still added for compatibility.
- Implement latest Graphite GitHub configuration guidelines.
- Sort apt dependencies alphabetically.
