[mod] migrate from Redis to Valkey (#4795)

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: HLFH <gaspard@dhautefeuille.eu>
Co-authored-by: Markus Heiser <markus.heiser@darmarit.de>

docs/admin/update-searxng.rst

@@ -56,7 +56,7 @@ SearXNG is growing rapidly, the services and opportunities are change every now
 and then, to name just a few:
 
 - Bot protection has been switched from filtron to SearXNG's :ref:`limiter
-  <limiter>`, this requires a :ref:`Redis <settings redis>` database.
+  <limiter>`, this requires a :ref:`Valkey <settings valkey>` database.
 
 - To save bandwidth :ref:`cache busting <static_use_hash>` has been implemented.
   To get in use, the ``static-expires`` needs to be set in the :ref:`uwsgi
@@ -89,5 +89,5 @@ to see if there are some left overs.  In this example there exists a *old*
    --------------
    ERROR: settings.yml in /etc/searx/ is deprecated, move file to folder /etc/searxng/
    ...
-   INFO    searx.redisdb                 : connecting to Redis db=0 path='/usr/local/searxng-redis/run/redis.sock'
-   INFO    searx.redisdb                 : connected to Redis
+   INFO    searx.valkeydb                 : connecting to Valkey db=0 path='/usr/local/searxng-valkey/run/valkey.sock'
+   INFO    searx.valkeydb                 : connected to Valkey