This works towards having reusable modules
* `config.pub-solar-os.networking.domain` is used for the main domain
* `config.pub-solar-os.privacyPolicUrl` links towards the privacy policy
* `config.pub-solar-os.imprintUrl` links towards the imprint
* `config.pub-solar-os.auth.enable` enables the keycloak installation.
This is needed because `config.pub-solar-os.auth` has to be available
everywhere, but we do not want to install keycloak everywhere.
* `config.pub-solar-os.auth.realm` sets the keycloak realm name
This commit changes the file structure around, so that we have the
following parts:
`/modules` contains reusable logic blocks for hosts.
`/hosts` contains host configurations.
`/lib` contains nix library functions.
`/overlays` contains overlay files.
`/public-keys` contains all information regarding public keys.
This change reduces the complexity of flake.nix, instead delegating this
out to the `default.nix` files in the above directories.