Download Unity CLI 1.0.0.20017

Highlights of 1.0.0-beta.17 (full notes at the release notes URL):
- unity plugin install and unity plugin upgrade warn you before they download a beta build of a plugin, so you know it isn't a stable release.
- A plugin can declare other plugins it needs.
- unity install --headless installs the headless Linux Editor, which runs with no display.
- unity pipeline automation apps versions create <app-id> --version <version> adds a draft version to a Pipeline Automation app, empty or copied from an existing version with --base-version.
- unity pipeline automation apps create creates a Pipeline Automation app and its first draft version from options, or from a JSON file with --file.
- unity pipeline cloud-build builds timeline <build-number> --build-target <target> shows how many seconds each phase of a build took, from waiting for a machine through upload.
- unity skill install installs the Unity skills from a newer release of the Unity-Technologies/skills repository.
- unity docs opens the common page for a bare name that several script reference pages share: unity docs Start opens MonoBehaviour.Start and unity docs Log opens Debug.Log, instead of a search.