allow configuring a target git repository for an applier

[bonzini]

Different importers can be run so that one importer only processes some projects. The simplest way to do this is to pass the target github repository to the importer via the Ansible config file, and from there to patchew-cli and then to applier-get.

applier-get must then filter projects according to their git.push_to property, and only return projects that match that property.

[bonzini]

• allow patchew apply --applier-mode to filter based on push URL
• allow patchew project update to filter based on push URL

For project update, this is just an optimization. Instead modifying the get-projects API endpoint to add a new argument, it's probably best to switch to the REST API.