fix(cache): unset client and user names in defaults (#8901)

# Which Problems Are Solved

By having default entries in the `Username` and `ClientName` fields, it
was not possible to unset there parameters. Unsetting them is required
for GCP connections

# How the Problems Are Solved

Set the fields to empty strings.

# Additional Changes

- none

# Additional Context

- none

(cherry picked from commit b77901cb4b)

cmd/defaults.yaml

@@ -211,11 +211,11 @@ Caches:
       # host:port address.
       Addr: localhost:6379
       # ClientName will execute the `CLIENT SETNAME ClientName` command for each conn.
-      ClientName: ZITADEL_cache
+      ClientName: ""
       # Use the specified Username to authenticate the current connection
       # with one of the connections defined in the ACL list when connecting
       # to a Redis 6.0 instance, or greater, that is using the Redis ACL system.
-      Username: zitadel
+      Username: ""
       # Optional password. Must match the password specified in the
       # requirepass server configuration option (if connecting to a Redis 5.0 instance, or lower),
       # or the User Password when connecting to a Redis 6.0 instance, or greater,