pgsql: Resume conflict-relevant data retention automatically.

Resume conflict-relevant data retention automatically.

This commit resumes automatic retention of conflict-relevant data for a
subscription. Previously, retention would stop if the apply process failed
to advance its xmin (oldest_nonremovable_xid) within the configured
max_retention_duration and user needs to manually re-enable
retain_dead_tuples option. With this change, retention will resume
automatically once the apply worker catches up and begins advancing its
xmin (oldest_nonremovable_xid) within the configured threshold.

Author: Zhijie Hou <houzj(dot)fnst(at)fujitsu(dot)com>
Reviewed-by: shveta malik <shveta(dot)malik(at)gmail(dot)com>
Reviewed-by: Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>
Reviewed-by: Dilip Kumar <dilipbalaut(at)gmail(dot)com>
Reviewed-by: Masahiko Sawada <sawada(dot)mshk(at)gmail(dot)com>
Discussion: https://postgr.es/m/OS0PR01MB5716BE80DAEB0EE2A6A5D1F5949D2@OS0PR01MB5716.jpnprd01.prod.outlook.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/0d48d393d465b6f1abe18b86bd5ac2de0636a40e

Modified Files
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doc/src/sgml/ref/create_subscription.sgml | 9 +-
src/backend/replication/logical/launcher.c | 10 +-
src/backend/replication/logical/worker.c | 200 ++++++++++++++++++++++-------
src/test/subscription/t/035_conflicts.pl | 27 ++++
4 files changed, 196 insertions(+), 50 deletions(-)