setup: Enable essential apps that use firewall

Tests in testing container:
- SSH, Service Discovery, and Web Server are shown as enabled on
Firewall page.
- FreedomBox interface can be accessed after disabling Cockpit.

Closes: #2016.

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

plinth/modules/apache/__init__.py

@@ -66,6 +66,7 @@ def setup(helper, old_version=None):
     actions.superuser_run(
         'apache',
         ['setup', '--old-version', str(old_version)])
+    helper.call('post', app.enable)
 
 
 # (U)ser (W)eb (S)ites

plinth/modules/avahi/__init__.py

@@ -98,6 +98,7 @@ def setup(helper, old_version=None):
     # available and require restart.
     helper.call('post', actions.superuser_run, 'service',
                 ['reload', 'avahi-daemon'])
+    helper.call('post', app.enable)
 
 
 def on_post_hostname_change(sender, old_hostname, new_hostname, **kwargs):

plinth/modules/ssh/__init__.py

@@ -68,6 +68,7 @@ class SSHApp(app_module.App):
 def setup(helper, old_version=None):
     """Configure the module."""
     actions.superuser_run('ssh', ['setup'])
+    helper.call('post', app.enable)
 
 
 def get_host_keys():