Add 'gel cli init-wsl' command

Our tests require a configured WSL instance, but you can't get one of these unless you call something requiring it (ie: `gel create instance`).

Ideally we would be able to force gel to create WSL without running any commands.

In addition, we should be able to provide an optional path to the gel executable to install in the container:

`gel cli init-wsl --cli-binary=...`