Valkey runs on the same spotahome RedisFailover operator as Redis and
speaks the same replication protocol and RDB format, so it needs no
strategy kind of its own. The only difference the backup Job sees is the
chart's resource-name prefix: valkey-<app> instead of redis-<app> for the
sentinel Service and the auth Secret.

The Redis driver now accepts applicationRef kind Valkey as well as Redis
and hands the template .Release.Prefix, derived from the app's kind, which
cozy-default-redis uses for every name it builds. A kind with no known
prefix fails the render instead of producing an empty one. cozy-default
routes apps.cozystack.io/Valkey to cozy-default-redis. A restore must
target an app of the same kind as the backup's source: replaying a Redis
dump into Valkey, or the reverse, is not something the strategy can
promise across engine releases.

The shipped template reads the prefix as `.Release.Prefix | default
"redis-"`: during an upgrade the previous controller, which has no Prefix
in its render context and serves only Redis, renders the new CR, and a
bare reference would print "<no value>" into the names.

The redis:8 image already loads RDB v11, which both shipped Valkey
versions (7.2, 8.1) write.

Signed-off-by: Andrey Kolkov <[email protected]>
Assisted-By: LLM
(cherry picked from commit 0c2f131)