charts/redpanda: v26.2.3

Changed

• Bump operator sidecar image tag to v26.2.3 release
• The default Redpanda version installed by the chart is now
  v26.2.2.

Fixed

• The sidecar's user watcher now sets the superusers cluster property once
  per sync pass, with the union of every users file, instead of once per file
  with only that file's users.
  Previously every sidecar start and every users-secret update transiently
  replaced the list with a partial one — kubelet's ..data symlink even
  parsed as an empty users file — momentarily revoking superuser status from
  connected clients. Only helm-chart deployments were affected; the operator
  deploys the sidecar with --no-set-superusers.
  The property is now written only when the list actually changes, so sidecar
  restarts no longer bump the cluster config version; when a users file can't
  be read, the patch is withheld and the pass retried with backoff instead of
  writing a partial list; and malformed users-file lines, which can contain
  passwords, are no longer echoed into the sidecar log.