[refactor] hostnames plugin: add fallback for old hostname_replace plugin

Co-authored-by: Markus Heiser <markus.heiser@darmarit.de>

searx/plugins/hostname_replace.py

@@ -0,0 +1,35 @@
+# SPDX-License-Identifier: AGPL-3.0-or-later
+# pylint: disable=missing-module-docstring
+
+from flask_babel import gettext
+from searx.plugins import logger
+
+name = gettext('Hostname replace')
+description = "Deprecated / contact system admin to configure 'Hostnames plugin'!!"
+default_on = False
+preference_section = 'general'
+
+plugin_id = 'hostname_replace'
+logger = logger.getChild(plugin_id)
+
+REPORTED = False
+
+
+def deprecated_msg():
+    global REPORTED  # pylint: disable=global-statement
+    if REPORTED:
+        return
+    logger.error(
+        "'Hostname replace' plugin is deprecated and will be dropped soon!"
+        " Configure 'Hostnames plugin':"
+        " https://docs.searxng.org/src/searx.plugins.hostnames.html"
+    )
+    REPORTED = True
+
+
+def on_result(_request, _search, result):
+    # pylint: disable=import-outside-toplevel, cyclic-import
+    from searx.plugins.hostnames import on_result as hostnames_on_result
+
+    deprecated_msg()
+    return hostnames_on_result(_request, _search, result)