register a repository package server as a device's update source
usage: fx add-update-source [--repo-name NAME] [--persist]
Configure target device to use a new update source.
--repo-name NAME Name of the repository package server to use as the update source.
--persist Enable persistence of repo metadata. Disabled by default.
NAME:
If no name is supplied, the name defaults to configured default repository.
Note:
This is a wrapper for `ffx target repository register`