pgsql: Sync PG_VERSION file in CREATE DATABASE.

Sync PG_VERSION file in CREATE DATABASE.

An OS crash could leave PG_VERSION empty or missing. The same symptom
appeared in a backup by block device snapshot, taken after the next
checkpoint and before the OS flushes the PG_VERSION blocks. Device
snapshots are not a documented backup method, however. Back-patch to
v15, where commit 9c08aea6a3090a396be334cc58c511edab05776a introduced
STRATEGY=WAL_LOG and made it the default.

Discussion: https://postgr.es/m/20240130195003.0a.nmisch@google.com

Branch
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REL_15_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/8fa4a1ac61189efffb8b851ee77e1bc87360c445

Modified Files
--------------
doc/src/sgml/monitoring.sgml | 5 +++++
src/backend/commands/dbcommands.c | 8 ++++++++
src/backend/utils/activity/wait_event.c | 3 +++
src/include/utils/wait_event.h | 3 ++-
4 files changed, 18 insertions(+), 1 deletion(-)