Mark quarkus-oidc-client-registration as experimental in doc

It's marked as experimental in the metadata of the extension but not in
the documentation.

docs/src/main/asciidoc/security-openid-connect-client-registration.adoc

@@ -9,6 +9,9 @@ include::_attributes.adoc[]
 :categories: security
 :topics: security,oidc,client
 :extensions: io.quarkus:quarkus-oidc-client-registration
+:extension-status: experimental
+
+include::{includes}/extension-status.adoc[]
 
 Typically, you have to register an OIDC client (application) manually in your OIDC provider's dashboard.
 During this process, you specify the human readable application name, allowed redirect and post logout URLs, and other properties.