apache: Enable dav and dav_fs modules

- DAV can simplify hosting the Feather Wiki app.

- It can also potentially be used to share folders over HTTP to clients such a
GNOME/KDE file mangers.

- Enabling the modules by default should have few disadvantages other than
slight increase in memory. It needs to be enabled with 'DAV on' directive on the
specific directories.

Tests:

- Running the service after patch run apache setup and the modules are enabled.

Signed-off-by: Sunil Mohan Adapa <sunil@medhas.org>

plinth/modules/apache/__init__.py

@@ -22,7 +22,7 @@ class ApacheApp(app_module.App):
 
     app_id = 'apache'
 
-    _version = 12
+    _version = 13
 
     def __init__(self) -> None:
         """Create components for the app."""

plinth/modules/apache/privileged.py

@@ -129,6 +129,11 @@ def setup(old_version: int):
         # enable users to share files uploaded to ~/public_html
         webserver.enable('userdir', kind='module')
 
+        # enable WebDAV protocol. Used by feather wiki and potentially by other
+        # apps and file sharing.
+        webserver.enable('dav', kind='module')
+        webserver.enable('dav_fs', kind='module')
+
         # setup freedombox site
         webserver.enable('freedombox', kind='config')
         webserver.enable('freedombox-tls', kind='config')