Add networking module

This adds a (for now hidden) clan network command that exposes list,
ping, overview subcommands to get informations about configured
networks.
ClanServices can now use the exports to define network specific
information.

This is not the complete feature yet, as we are lacking more tests and
documentation, but merging this now makes it easier to iterate.

clanServices/internet/default.nix

@@ -0,0 +1,47 @@
+{ ... }:
+{
+  _class = "clan.service";
+  manifest.name = "clan-core/internet";
+  manifest.description = "direct access (or via ssh jumphost) to machines";
+  manifest.categories = [
+    "System"
+    "Network"
+  ];
+  roles.default = {
+    interface =
+      { lib, ... }:
+      {
+        options = {
+          host = lib.mkOption {
+            type = lib.types.str;
+            description = ''
+              ip address or hostname (domain) of the machine
+            '';
+          };
+          jumphosts = lib.mkOption {
+            type = lib.types.listOf lib.types.str;
+            default = [ ];
+            description = ''
+              optional list of jumphosts to use to connect to the machine
+            '';
+          };
+        };
+      };
+    perInstance =
+      {
+        roles,
+        lib,
+        settings,
+        ...
+      }:
+      {
+        exports.networking = {
+          # TODO add user space network support to clan-cli
+          peers = lib.mapAttrs (_name: machine: {
+            host.plain = machine.settings.host;
+            SSHOptions = map (_x: "-J x") machine.settings.jumphosts;
+          }) roles.default.machines;
+        };
+      };
+  };
+}