refactor gitea configuration in a module

updated: modules/gitea to put specific configuration in the module
updated: flake.nix to import the module in nodes

modules/gitea/n100/default.nix

@@ -0,0 +1,7 @@
+{nodes, ...}:{
+  networking.nat.forwardPorts = [{
+    sourcePort = nodes.zimablade.config.services.gitea.settings.server.SSH_PORT;
+    proto = "tcp";
+    destination = "10.0.0.4:22";  
+  }];
+}