Adding nss-mdns for Avahi mDNS for local domain resolving etc.

Now only modifiying /etc/nsswitch.conf is necesarry. https://wiki.archlinux.org/title/Avahi#systemd-resolved_prevents_nss-mdns_from_working

Fixes #80

mkosi.conf.d/20-packages-network.conf

@@ -5,4 +5,5 @@
 Packages=bind
          iproute2
          nfs-utils
+         nss-mdns # Needed for Avahi mDNS for local domain resolving etc.
          ufw # Simple firewall; consider switching to firewalld once the KCM supports zones

mkosi.finalize.d/00-modify_nsswitch.py

@@ -0,0 +1,57 @@
+# SPDX-License-Identifier: GPL-2.0-only OR GPL-3.0-only OR LicenseRef-KDE-Accepted-GPL
+# SPDX-FileCopyrightText: 2025 Hadi Chokr <hadichokr@icloud.com>
+
+import os
+import sys
+
+def modify_nsswitch():
+    path = "/etc/nsswitch.conf"
+    
+    print(f"Checking {path}...")  # Debug line
+    
+    # Read the file
+    try:
+        with open(path, "r") as file:
+            lines = file.readlines()
+    except Exception as e:
+        print(f"Error reading {path}: {e}", file=sys.stderr)
+        raise  # Re-raise the exception
+
+    modified = False
+
+    # Process each line
+    for i, line in enumerate(lines):
+        print(f"Checking line: {line.strip()}")  # Debug line
+        if line.startswith("hosts:"):
+            if "mymachines" in line and "mdns_minimal" not in line:
+                lines[i] = line.replace("mymachines", "mymachines mdns_minimal [NOTFOUND=return]", 1)
+                modified = True
+                print("Added mdns_minimal after mymachines.")  # Debug line
+            elif "mymachines" not in line and "mdns_minimal" not in line:
+                lines[i] = line.replace("hosts:", "hosts: mdns_minimal [NOTFOUND=return] ", 1)
+                modified = True
+                print("Added mdns_minimal.")  # Debug line
+            break
+
+    if not modified:
+        raise RuntimeError("Expected modification but no changes were made.")
+
+    # Write back the modified file
+    try:
+        with open(path, "w") as file:
+            file.writelines(lines)
+        print("Updated /etc/nsswitch.conf")
+    except Exception as e:
+        print(f"Error writing to {path}: {e}", file=sys.stderr)
+        raise  # Re-raise the exception
+
+if __name__ == "__main__":
+    if os.geteuid() != 0:
+        print("This script must be run as root.", file=sys.stderr)
+        sys.exit(1)
+    
+    try:
+        modify_nsswitch()
+    except Exception as e:
+        print(f"Fatal error: {e}", file=sys.stderr)
+        sys.exit(1)