Host pull requests

[brokenpylons]

It would be nice if the pull requests on the development repos were deployed as well.

1. The pull requests need to be fetched from GitHub API with the branch info and stored as JSON.
2. The JSON is read in nix, for each pull request the repo is fetched followed by getFlake extracting the NixOS module.
3. Each NixOS module is deployed to a separate systemd-nspawn container, link. The package must be built with --base-href as /dev/branch_name, link, so it needs to be an option you override in the NixOS module and pacakge.
4. Add a nginx service which will forward the /dev/branch_name to the container.
5. Forward the /dev/* on the gateway.
6. Add an action to the development repo which will trigger a refresh of the JSON here and deploy.

[brokenpylons]

The same set of options will need to work for all imported modules. They don't change that much so that shouldn't be an issue.