Document new wsrep_mode settings

Introduced two new wsrep_mode options

• REPLICATE_MYISAM
• REPLICATE_ARIA

Deprecated wsrep_replicate_myisam parameter and we use wsrep_mode = REPLICATE_MYISAM instead.

These new options will allow Galera to replicate both DDL and DML for MyISAM [and,or] Aria using TOI .e.g.

SET GLOBAL wsrep_mode = "REQUIRED_PRIMARY_KEY,REPLICATE_MYISAM,REPLICATE_ARIA";

Will replicate both MyISAM and Aria DML but requires primary key for replicated table.