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

Tests:

- Config files are all symlinks in /etc/
- Web interface works

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

debian/freedombox.maintscript

@@ -136,3 +136,4 @@ rm_conffile /etc/fail2ban/jail.d/ssh-freedombox.conf 23.10~
 rm_conffile /etc/avahi/services/sftp-ssh.service 23.10~
 rm_conffile /etc/avahi/services/ssh.service 23.10~
 rm_conffile /etc/apache2/includes/freedombox-single-sign-on.conf 23.10~
+rm_conffile /etc/apache2/conf-available/syncthing-plinth.conf 23.10~

plinth/modules/syncthing/__init__.py

@@ -5,6 +5,7 @@ from django.utils.translation import gettext_lazy as _
 
 from plinth import app as app_module
 from plinth import cfg, frontpage, menu
+from plinth.config import DropinConfigs
 from plinth.daemon import Daemon
 from plinth.modules.apache.components import Webserver
 from plinth.modules.backups.components import BackupRestore
@@ -42,7 +43,7 @@ class SyncthingApp(app_module.App):
 
     app_id = 'syncthing'
 
-    _version = 6
+    _version = 7
 
     DAEMON = 'syncthing@syncthing'
 
@@ -79,6 +80,11 @@ class SyncthingApp(app_module.App):
         packages = Packages('packages-syncthing', ['syncthing'])
         self.add(packages)
 
+        dropin_configs = DropinConfigs('dropin-configs-syncthing', [
+            '/etc/apache2/conf-available/syncthing-plinth.conf',
+        ])
+        self.add(dropin_configs)
+
         firewall = Firewall('firewall-syncthing-web', info.name,
                             ports=['http', 'https'], is_external=True)
         self.add(firewall)