Unset bootstrap credentials before exec-ing the server

POSTGRES_PASSWORD (and related vars) are only needed during initdb and
the temporary-server initialisation phase. After that they serve no
purpose, but remain in the process environment for the entire lifetime
of the container, where any loaded C extension can read them via
environ.

Unsetting them immediately before the final exec ensures the running
PostgreSQL server process starts with a clean environment.

Author: mkindahl

docker-entrypoint.sh

@@ -379,6 +379,7 @@ _main() {
 		fi
 	fi
 
+	unset POSTGRES_PASSWORD POSTGRES_USER POSTGRES_DB POSTGRES_INITDB_ARGS
 	exec "$@"
 }