GitHub Actions CI

Actions

custom-actions/build-packager: Builds Shaka Packager. Leaves build artifacts in the "artifacts" folder. Requires OS-dependent and build-dependent inputs.
custom-actions/test-packager: Tests Shaka Packager. Requires OS-dependent and build-dependent inputs.
custom-actions/build-docs: Builds Shaka Packager docs.

On PR:
- build_and_test.yaml: Builds and tests all combinations of OS & build settings. Also builds docs.
On release tag:
- github_release.yaml: Creates a draft release on GitHub, builds and tests all combinations of OS & build settings, builds docs on all OSes, attaches static release binaries to the draft release, then fully publishes the release.
On release published:
- docker_hub_release.yaml: Builds a Docker image to match the published GitHub release, then pushes it to Docker Hub.
- npm_release.yaml: Builds an NPM package to match the published GitHub release, then pushes it to NPM.
- update_docs.yaml: Builds updated docs and pushes them to the gh-pages branch.

DOCKERHUB_CI_USERNAME: The username of the Docker Hub CI account
DOCKERHUB_CI_TOKEN: An access token for Docker Hub
- To generate, visit https://hub.docker.com/settings/security
NPM_CI_TOKEN: An "Automation"-type access token for NPM for the shaka-bot account
- To generate, visit https://www.npmjs.com/settings/shaka-bot/tokens and select the "Automation" type
SHAKA_BOT_TOKEN: A GitHub personal access token for the shaka-bot account, with workflow scope
- To generate, visit https://github.com/settings/tokens/new and select the workflow scope