doc: Add missing backend_type to pg_stat_activity
Commit
0c679464a8 added the missing backendDesc for B_STANDALONE_BACKEND
but missed updating the list of backend types in the documentation. Fix
by adding it to the list.
Author: Noriyoshi Shinoda <noriyoshi.shinoda@hpe.com>
Discussion: https://postgr.es/m/DM4PR84MB1734ECEA02BCB59564E8FC03EE4A9@DM4PR84MB1734.NAMPRD84.PROD.OUTLOOK.COM