Re: Add a GUC variable that control logical replication

Sybase has a feature to turn off replication at the session level: set
replication = off, which can be temporarily turned off when there is a
maintenance action on the table. Our users also want this feature.
I add a new flag bit in xinfo, control it with a session-level variable,
when set to true, this flag is written when the transaction is
committed, and when the logic is decoded it abandons the transaction
like aborted transactions. Since PostgreSQL has two types of
replication, I call the variable "logical_replication" to avoid
confusion and default value is true.