Some of our inference providers support passthrough authentication via
`x-llamastack-provider-data` header values. This fixes the providers
that support passthrough auth to not cache their clients to the
backend providers (mostly OpenAI client instances) so that the client
connecting to Llama Stack has to provide those auth values on each and
every request.
Signed-off-by: Ben Browning <bbrownin@redhat.com>
