Missing end_session endpoint

Hi there, I have used this plugin to connect a Keycloak to Wordpress. It would be important to ensure that if a user logs out, they are logged out from the connected client, Keycloak and the Wordpress in this szenario. Sadly this does not work for the Wordpress part and i came to realize that the plugin does not actually provide such an endpoint in the first place, so this option couldn't be activated for the IDP.

Would be a great addition to this otherwise wonderfully working plugin. :)

Start by locating the plugin's existing endpoint registration and logout handling, then trace how WordPress and the connected Keycloak client currently process logout. Done means an end_session endpoint exists and supports logging the user out from the connected client, Keycloak, and WordPress so the option can be activated for the IDP.

Written by the indexing model from the issue text.