cli: Treat first argument as name of release channel to use for the cli (#10856)

With this commit, it is now possible to invoke cli with a release
channel of bundle as an argument. E.g: `zed stable some_arguments` will
find CLI binary of Stable channel installed on your machine and invoke
it with `some_arguments` (so the first argument is essentially omitted).

Fixes #10851

Release Notes:

- CLI now accepts an optional name of release channel as it's first
argument. For example, `zed stable` will always use your Stable
installation's CLI. Trailing args are passed along.