Support multiple install methods for a single binary

In order to make more flexible binny configurations, while remaining performant, it would be useful to support multiple installation methods.

An example that needs this is: installing `gh` on FreeBSD. Today, there is no binary published for FreeBSD, so a user would need to use the `go-install` method for portability. However, the `go-install` method is slow since it needs to download all dependencies and run a complete go build. It would be preferable to attempt to download a binary using the `github-release` method, and if that failed to fall back to a `go-install`.

Trace the existing github-release and go-install methods and how a binary selects its installation method. Determine how an ordered fallback can remain performant, then verify that a binary can try github-release and use go-install when no compatible release is available, with tests covering both outcomes.

Written by the indexing model from the issue text.