It is not possible to update config (AuthenticatorConfigRepresentation) of execution in auth flow.

There is also no update method in org.keycloak.admin.client.resource.AuthenticationManagementResource. There is just newExecutionConfig.

Steps to reproduce in admin console:
1. go to console - authentication - flows
2. create new flow
3. create new execution within the flow
4. create authenticator config
5. try to update the config
6. unexpected error message is shown and log says ERROR [org.jboss.resteasy.resteasy_jaxrs.i18n] (default task-8) RESTEASY002010: Failed to execute: javax.ws.rs.NotAllowedException: RESTEASY003650: No resource method found for PUT, return 405 with Allow header
...