[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>

docs/dev/lxcdev.rst

@@ -140,7 +140,7 @@ proxy :ref:`installation nginx` into the archlinux container run:
 .. sidebar:: Fully functional SearXNG suite
 
    From here on you have a fully functional SearXNG suite (including a
-   :ref:`redis db`).
+   :ref:`valkey db`).
 
 In such a SearXNG suite admins can maintain and access the debug log of the
 services quite easy.