server-2020-10-02

Release channels and staged releases for the manager (#736)

* Generate all updates files

* TEST

* Allow staged releases and beta channels for all Electron platforms

* Clarify manager_release_channel.sh

* Install jq in the CI build

* Use a common script for common packaging options

* Fix comment in get_packaging_opts

* Use a version of `jq` managed by Yarn

* Make staged rollouts affect the beta channel for mainline builds

Also remove the alpha info chanel files since we aren't using them.

* Fix packaging scripts when no args are passed

* Don't install jq in Travis anymore

* Fix trailing newlines

* Fill packaging options by `source`-ing the options parsing script

* Rename to get_manager_release_channel.sh