Make invalid primary_slot_name follow standard GUC error reporting.

Make invalid primary_slot_name follow standard GUC error reporting.

Previously, if primary_slot_name was set to an invalid slot name and
the configuration file was reloaded, both the postmaster and all other
backend processes reported a WARNING. With many processes running,
this could produce a flood of duplicate messages. The problem was that
the GUC check hook for primary_slot_name reported errors at WARNING
level via ereport().

This commit changes the check hook to use GUC_check_errdetail() and
GUC_check_errhint() for error reporting. As with other GUC parameters,
this causes non-postmaster processes to log the message at DEBUG3,
so by default, only the postmaster's message appears in the log file.

Backpatch to all supported versions.

Author: Fujii Masao <[email protected]>
Reviewed-by: Chao Li <[email protected]>
Reviewed-by: Amit Kapila <[email protected]>
Reviewed-by: Álvaro Herrera <[email protected]>
Reviewed-by: Hayato Kuroda <[email protected]>
Discussion: https://postgr.es/m/CAHGQGwFud-cvthCTfusBfKHBS6Jj6kdAPTdLWKvP2qjUX6L_wA@mail.gmail.com
Backpatch-through: 13