docs(volcengine): mark referent authentication as supported (#6584)
The Volcengine provider resolves its auth secret references through
resolvers.SecretKeyRef and validates them with the relaxed
ValidateReferentSecretSelector, so a namespace-less ClusterSecretStore
reference resolves against the ExternalSecret namespace. Mark the
referent authentication cell in the support matrix accordingly.
Signed-off-by: Alexander Chernov <alexander@chernov.it>
Alexander Chernov