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

Tests:

- Config files are all symlinks in /etc/

- fail2ban-client show shows sshd in jail list

- When ssh is enabled avahi-browse -a shows SSH and SFTP services. The avahi
service files are created in /etc/avahi/services/. When service is disabled,
files are removed and avahi-browse -a does not show the services.

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

debian/freedombox.maintscript

@@ -132,3 +132,6 @@ rm_conffile /etc/apache2/conf-available/searx-freedombox.conf 23.10~
 rm_conffile /etc/fail2ban/fail2ban.d/freedombox.conf 23.10~
 rm_conffile /etc/fail2ban/jail.d/freedombox.conf 23.10~
 rm_conffile /etc/apache2/includes/freedombox-sharing.conf 23.10~
+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~

plinth/modules/ssh/__init__.py

@@ -9,6 +9,7 @@ from django.utils.translation import gettext_lazy as _
 
 from plinth import app as app_module
 from plinth import menu
+from plinth.config import DropinConfigs
 from plinth.daemon import Daemon
 from plinth.modules.backups.components import BackupRestore
 from plinth.modules.firewall.components import Firewall
@@ -30,7 +31,7 @@ class SSHApp(app_module.App):
 
     app_id = 'ssh'
 
-    _version = 3
+    _version = 4
 
     def __init__(self):
         """Create components for the app."""
@@ -50,6 +51,17 @@ class SSHApp(app_module.App):
         packages = Packages('packages-ssh', ['openssh-server'])
         self.add(packages)
 
+        dropin_configs = DropinConfigs('dropin-configs-ssh', [
+            '/etc/fail2ban/jail.d/ssh-freedombox.conf',
+        ])
+        self.add(dropin_configs)
+
+        dropin_configs = DropinConfigs('dropin-config-ssh-avahi', [
+            '/etc/avahi/services/sftp-ssh.service',
+            '/etc/avahi/services/ssh.service',
+        ], copy_only=True)
+        self.add(dropin_configs)
+
         firewall = Firewall('firewall-ssh', info.name, ports=['ssh'],
                             is_external=True)
         self.add(firewall)