pgsql: Disallow server start with sync_replication_slots = on and wal_l

Disallow server start with sync_replication_slots = on and wal_level < logical.

Replication slot synchronization (sync_replication_slots = on)
requires wal_level to be logical. This commit prevents the server
from starting if sync_replication_slots is enabled but wal_level
is set to minimal or replica.

Failing early during startup helps users catch invalid configurations
immediately, which is important because changing wal_level requires
a server restart.

Author: Fujii Masao <masao(dot)fujii(at)gmail(dot)com>
Reviewed-by: Shveta Malik <shveta(dot)malik(at)gmail(dot)com>
Discussion: https://postgr.es/m/CAH0PTU_pc3oHi__XESF9ZigCyzai1Mo3LsOdFyQA4aUDkm01RA@mail.gmail.com

Branch
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master

Details
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https://git.postgresql.org/pg/commitdiff/12da45742cfd15d9fab151b25400d96a1febcbde

Modified Files
--------------
src/backend/postmaster/postmaster.c | 3 +++
1 file changed, 3 insertions(+)