Improve error message for pg_create_subscription.

c3afe8c updated this error message, but it didn't use the new
style established in de4d456.

Reviewed-by: Tom Lane
Discussion: https://postgr.es/m/20230512203721.GA2644063%40nathanxps13.home

Author: nathan-bossart

src/backend/commands/subscriptioncmds.c

@@ -611,7 +611,9 @@ CreateSubscription(ParseState *pstate, CreateSubscriptionStmt *stmt,
 	if (!has_privs_of_role(owner, ROLE_PG_CREATE_SUBSCRIPTION))
 		ereport(ERROR,
 				(errcode(ERRCODE_INSUFFICIENT_PRIVILEGE),
-				 errmsg("must have privileges of pg_create_subscription to create subscriptions")));
+				 errmsg("permission denied to create subscription"),
+				 errdetail("Only roles with privileges of the \"%s\" role may create subscriptions.",
+						   "pg_create_subscription")));
 
 	/*
 	 * Since a subscription is a database object, we also check for CREATE

src/test/regress/expected/subscription.out

@@ -79,7 +79,8 @@ ERROR:  subscription "regress_testsub" already exists
 -- fail - must be superuser
 SET SESSION AUTHORIZATION 'regress_subscription_user2';
 CREATE SUBSCRIPTION regress_testsub2 CONNECTION 'dbname=regress_doesnotexist' PUBLICATION foo WITH (connect = false);
-ERROR:  must have privileges of pg_create_subscription to create subscriptions
+ERROR:  permission denied to create subscription
+DETAIL:  Only roles with privileges of the "pg_create_subscription" role may create subscriptions.
 SET SESSION AUTHORIZATION 'regress_subscription_user';
 -- fail - invalid option combinations
 CREATE SUBSCRIPTION regress_testsub2 CONNECTION 'dbname=regress_doesnotexist' PUBLICATION testpub WITH (connect = false, copy_data = true);