Nearly completely replace the original GitHub actions workflow.
Changes:

- Move from `.sh` files in `ci/steps` to steps in the workflow.
- Move from using docker images for environment to manual setup.
- Upgrade nfpm to v2.3.1

BREAKING CHANGE: official arm64 builds no longer support CentOS 7.
If you need to use CentOS 7 on arm64, build `code-server` locally.
For docs, see the yarn/npm section in `docs/install.md`.