Docs - updates for PL/Container 3 beta (#9773)
Docs - updates for PL/Container 3 beta (#9773)

* Docs - updates for PL/Container 3 beta

* Update to account for beta being available for Ubuntu

* Update install, uninstall tasks for 3 Beta

* Qualify r image as beta
adam8157/gpdb,adam8157/gpdb,adam8157/gpdb,lisakowen/gpdb,greenplum-db/gpdb,jmcatamney/gpdb,jmcatamney/gpdb,adam8157/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,50wu/gpdb,jmcatamney/gpdb,adam8157/gpdb,50wu/gpdb,jmcatamney/gpdb,xinzweb/gpdb,adam8157/gpdb,lisakowen/gpdb,adam8157/gpdb,50wu/gpdb,xinzweb/gpdb,lisakowen/gpdb,jmcatamney/gpdb,greenplum-db/gpdb,xinzweb/gpdb,lisakowen/gpdb,jmcatamney/gpdb,50wu/gpdb,50wu/gpdb,adam8157/gpdb,lisakowen/gpdb,xinzweb/gpdb,xinzweb/gpdb,xinzweb/gpdb,lisakowen/gpdb,50wu/gpdb,50wu/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,lisakowen/gpdb,lisakowen/gpdb,greenplum-db/gpdb,greenplum-db/gpdb,xinzweb/gpdb,50wu/gpdb,xinzweb/gpdb,jmcatamney/gpdb