WIP [skip ci]

Signed-off-by: Salvatore Martire <[email protected]>

developer_manual/app_development/dav_properties.rst

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+====
+Apps DAV Properties
+====
+
+Add description of what DAV properties are and link SabreDAV.
+
+Registering a DAV plugin
+--------
+
+Adding/registering a new property
+--------
+
+Preloading properties for better performance
+--------
+
+When properties are listed for files, your plugin will need to load the property from the storage and return it. This
+becomes quickly an issue for directories with many files as the plugin may issue one or more queries per file and reduce
+Nextcloud's performance. To avoid this, a convenience event `preloadCollection` is emitted by the DAV server for
+nodes of type collection, whenever properties are being loaded for all files inside a collection.
+
+Following the example above to register a DAV plugin, you can do the same to register the same plugin to preload the
+data your application needs.
+
+# TODO add example snippet
+