networks: Use drop-in config component for /etc files

Tests:

- Config files are all symlinks in /etc/
- Network manager does run the dispatcher script due to write permission for
  group. This issue is unrelated to the patch, however.

Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>
Reviewed-by: James Valleroy <jvalleroy@mailbox.org>

debian/freedombox.maintscript

@@ -120,3 +120,4 @@ rm_conffile /etc/fail2ban/filter.d/matrix-auth-freedombox.conf 23.10~
 rm_conffile /etc/apache2/conf-available/mediawiki-freedombox.conf 23.10~
 rm_conffile /etc/mediawiki/FreedomBoxStaticSettings.php 23.10~
 rm_conffile /etc/apache2/conf-available/minidlna-freedombox.conf 23.10~
+rm_conffile /etc/NetworkManager/dispatcher.d/10-freedombox-batman 23.10~

plinth/modules/networks/__init__.py

@@ -8,6 +8,7 @@ from django.utils.translation import gettext_lazy as _
 
 from plinth import app as app_module
 from plinth import daemon, kvstore, menu, network
+from plinth.config import DropinConfigs
 from plinth.package import Packages
 
 from . import privileged
@@ -45,7 +46,7 @@ class NetworksApp(app_module.App):
 
     app_id = 'networks'
 
-    _version = 1
+    _version = 2
 
     can_be_disabled = False
 
@@ -66,6 +67,11 @@ class NetworksApp(app_module.App):
         packages = Packages('packages-networks', ['network-manager', 'batctl'])
         self.add(packages)
 
+        dropin_configs = DropinConfigs('dropin-configs-networks', [
+            '/etc/NetworkManager/dispatcher.d/10-freedombox-batman',
+        ])
+        self.add(dropin_configs)
+
     def diagnose(self):
         """Run diagnostics and return the results."""
         results = super().diagnose()