[mod] typification of the preference settings

no functional change / except the missing online doc which is now available::

    $ make docs.live
    $ xdg-open "http://127.0.0.1:8000/admin/settings/settings_preferences.html"

Signed-off-by: Markus Heiser <markus.heiser@darmarit.de>

searx/_settings.py

@@ -0,0 +1,42 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
+"""Implementation of the :py:obj:`preference <searx.preference>` settings."""
+# pylint: disable = too-few-public-methods
+
+import typing as t
+import msgspec
+
+
+class SettingsPref(msgspec.Struct, kw_only=True, forbid_unknown_fields=True):
+    """Options for configuring the preferences
+
+    .. code:: yaml
+
+       preferences:
+         lock:
+           - favicon_resolver
+           - image_proxy
+           - method
+       # ...
+
+    """
+
+    lock: set[
+        t.Literal[
+            "categories",
+            "language",
+            "locale",
+            "autocomplete",
+            "favicon_resolver",
+            "image_proxy",
+            "method",
+            "safesearch",
+            "theme",
+            "results_on_new_tab",
+            "doi_resolver",
+            "simple_style",
+            "center_alignment",
+            "query_in_title",
+            "search_on_category_select",
+        ]
+    ] = set()
+    """Lock arbitrary settings on the preferences page."""