pgsql: Rename standby_slot_names to synchronized_standby_slots.

Rename standby_slot_names to synchronized_standby_slots.

The standby_slot_names GUC allows the specification of physical standby
slots that must be synchronized before the logical walsenders associated
with logical failover slots. However, for this purpose, the GUC name is
too generic.

Author: Hou Zhijie
Reviewed-by: Bertrand Drouvot, Masahiko Sawada
Backpatch-through: 17
Discussion: https://postgr.es/m/ZnWeUgdHong93fQN@momjian.us

Branch
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REL_17_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/0f934b0739ad28e8e20d8ad22ca80538544ce28a

Modified Files
--------------
doc/src/sgml/config.sgml | 12 +--
doc/src/sgml/func.sgml | 4 +-
doc/src/sgml/logical-replication.sgml | 2 +-
doc/src/sgml/logicaldecoding.sgml | 8 +-
doc/src/sgml/release-17.sgml | 2 +-
src/backend/replication/logical/slotsync.c | 4 +-
src/backend/replication/slot.c | 119 +++++++++++----------
src/backend/replication/walsender.c | 4 +-
src/backend/utils/misc/guc_tables.c | 6 +-
src/backend/utils/misc/postgresql.conf.sample | 4 +-
src/include/replication/slot.h | 4 +-
src/include/replication/walsender_private.h | 4 +-
src/include/utils/guc_hooks.h | 6 +-
.../recovery/t/040_standby_failover_slots_sync.pl | 48 +++++----
src/tools/pgindent/typedefs.list | 2 +-
15 files changed, 116 insertions(+), 113 deletions(-)