Document group_replication_xcom_ssl_socket_timeout and group_replication_xcom_ssl_accept_retries

We introduced two new server variables, group_replication_xcom_ssl_socket_timeout and group_replication_xcom_ssl_accept_retries as part of PS-8592 that will be released in 8.0.34. Both these new variables need to be documented in https://docs.percona.com/percona-server/8.0/replication/group-replication-system-variables.html

 

Description about these variable is as follows

 

    1. group_replication_xcom_ssl_socket_timeout
    
       It is a file-descriptor level timeout in seconds for both accept() and
       SSL_accept() calls when group replication is listening on the xcom port.
       When set to a valid value, say for example 5 seconds, both accept() and
       SSL_accept() return after 5 seconds. The default value has been set to 0
       (waits infinitely) for backward compatibility. This variable is effective
       only when GR is configred with SSL.
    
    2. group_replication_xcom_ssl_accept_retries
    
       It defines the number of retries to be performed before closing the socket.
       For each retry the server thread calls SSL_accept()  with timeout defined by
       the group_replication_xcom_ssl_socket_timeout for the SSL handshake process
       once the connection has been accepted by the first accept() call. The
       default value has been set to 10. This variable is effective only when GR is
       configred with SSL.
    
   
   Both of the above variables are dynamically configurable, but will become
   effective only on START GROUP_REPLICATION.