[EO] Document that some credentials for Wildfly Elytron Client are unsupported in EAP 7.1

Based on comments in JBEAP-11720 (see description of JBEAP-11720 as well as JBEAP-11760 and related comments) some credentials from configuration.authentication-client.authentication-configurations.configuration.credentials element in Wildfly Elytron client configuration file are unsupported. They currently occur in this configuration file for usage with experimental mechanisms. Elytron implementation currently does not provide any of these mechanisms.

Following credentials from configuration.authentication-client.authentication-configurations.configuration.credentials element in Wildfly Elytron client configuration which are unsupported:

• key-pair
• public-key-pem
• key-store-reference
• certificate

This should be documented in section which describes elements of Wildfly Elytron client configuration file.