Release channel support

[pirog]

We should allow users to opt-into a more frequent/bleeding edge release channel.

There are a few pieces to this:

1. The release channel needs to be a user setting that can be read by the desktop application and potentially other things like lando/hyperdrive. lando currently stores the release channel in the config.yml.
2. The above setting then needs to map onto various update sources eg the "beta" channel in teh electron updater, a "beta" or alternate "release" tag for our plugins and NPM dependencies and likely a "beta/prerelease" for CLI things. That means that when the user toggles on "edge" release mode they get edge releases for ALL THE STUFF: desktop application, CLIs and plugins.

Im guessing we probably want to wait on this until

1. We have figured out how each thing will handle its own "stable" and "edge" releases and we have a unified package to get info about them.
2. We have some sort of settings/config management in the electron GUI