[mod] migrate from Redis to Valkey

This patch migrates from `redis==5.2.1` [1] to `valkey==6.1.0` [2].

The migration to valkey is necessary because the company behind Redis has decided
to abandon the open source license. After experiencing a drop in user numbers,
they now want to run it under a dual license again. But this move demonstrates
once again how unreliable the company is and how it treats open source
developers.

To review first, read the docs::

    $ make docs.live

Follow the instructions to remove redis:

- http://0.0.0.0:8000/admin/settings/settings_redis.html

Config and install a local valkey DB:

- http://0.0.0.0:8000/admin/settings/settings_valkey.html

[1] https://pypi.org/project/redis/
[2] https://pypi.org/project/valkey/

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

searx/webapp.py

@@ -118,7 +118,7 @@ from searx.locales import (
 from searx.autocomplete import search_autocomplete, backends as autocomplete_backends
 from searx import favicons
 
-from searx.redisdb import initialize as redis_initialize
+from searx.valkeydb import initialize as valkey_initialize
 from searx.sxng_locales import sxng_locales
 import searx.search
 from searx.network import stream as http_stream, set_context_network_name
@@ -1397,7 +1397,7 @@ def init():
         return
 
     locales_initialize()
-    redis_initialize()
+    valkey_initialize()
     searx.plugins.initialize(app)
 
     metrics: bool = get_setting("general.enable_metrics")  # type: ignore