[Feature request] Ability to opt-in to Mullvad Browser pre-releases from the built-in updater UI

[duck09]

title.

[ruihildt]

Pre-releases correspond to Mullvad Browser Alpha

If you wish, you can install it in parallel to Mullvad Browser, and it will auto-update when new versions are out. We haven't made it public, because we want to change the startpage to make it clearer you're not using the stable release.
Once this is done, we'll also add it to our deb/rpm repositories.

This is planned for the coming weeks.

Though you won't be able to opt-in directly from the stable Mullvad Browser.