Store 2PC GID in commit/abort WAL recs for logical decoding

Store 2PC GID in commit/abort WAL recs for logical decoding

Store GID of 2PC in commit/abort WAL records when wal_level = logical.
This allows logical decoding to send the SAME gid to subscribers
across restarts of logical replication.

Track relica origin replay progress for 2PC.

(Edited from patch 0003 in the logical decoding 2PC series.)

Authors: Nikhil Sontakke, Stas Kelvich
Reviewed-by: Simon Riggs, Andres Freund