refactor: split server modules into smaller more manageable files

modules/nixos-modules/server/paperless/database.nix

@@ -0,0 +1,34 @@
+{
+  config,
+  lib,
+  ...
+}: {
+  config = lib.mkIf config.services.paperless.enable (lib.mkMerge [
+    {
+      host = {
+        postgres = {
+          enable = true;
+        };
+      };
+    }
+    (
+      lib.mkIf config.host.postgres.enable {
+        host = {
+          postgres = {
+            extraUsers = {
+              ${config.services.paperless.database.user} = {
+                isClient = true;
+                createUser = true;
+              };
+            };
+            extraDatabases = {
+              ${config.services.paperless.database.user} = {
+                name = config.services.paperless.database.user;
+              };
+            };
+          };
+        };
+      }
+    )
+  ]);
+}