Make /opt/moonarch root-owned for multi-user support

Remove chown from archinstall custom-commands so the repo stays
root:root. Use sudo for git operations in update.sh. Any user with
sudo can now run moonarch-update without owning the repo.

config/user_configuration.json

@@ -70,7 +70,6 @@
     "timezone": "Europe/Berlin",
 
     "custom-commands": [
-        "git clone https://gitea.moonarch.de/nevaforget/moonarch.git /opt/moonarch",
-        "chown -R 1000:1000 /opt/moonarch"
+        "git clone https://gitea.moonarch.de/nevaforget/moonarch.git /opt/moonarch"
     ]
 }