Add missing index terms for replication commands in the document.
Add missing index terms for replication commands in the document.

Previously only CREATE_REPLICATION_SLOT was exposed as an index term.
That's odd and there is no reason not to add index terms for other
replication commands.

Back-patch to 9.4.

ashwinstar/gpdb,jmcatamney/gpdb,lisakowen/gpdb,50wu/gpdb,xinzweb/gpdb,adam8157/gpdb,50wu/gpdb,greenplum-db/gpdb,lisakowen/gpdb,50wu/gpdb,adam8157/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,lisakowen/gpdb,50wu/gpdb,xinzweb/gpdb,adam8157/gpdb,jmcatamney/gpdb,xinzweb/gpdb,50wu/gpdb,ashwinstar/gpdb,ashwinstar/gpdb,ashwinstar/gpdb,lisakowen/gpdb,adam8157/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,adam8157/gpdb,jmcatamney/gpdb,adam8157/gpdb,greenplum-db/gpdb,lisakowen/gpdb,adam8157/gpdb,lisakowen/gpdb,xinzweb/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,50wu/gpdb,xinzweb/gpdb,lisakowen/gpdb,ashwinstar/gpdb,xinzweb/gpdb,xinzweb/gpdb,adam8157/gpdb,greenplum-db/gpdb,50wu/gpdb,ashwinstar/gpdb,jmcatamney/gpdb,50wu/gpdb,greenplum-db/gpdb,ashwinstar/gpdb,lisakowen/gpdb,jmcatamney/gpdb,xinzweb/gpdb