Add String object access hooks

This caters for cases where the access is to an object identified by
name rather than Oid.

The first user of these is the GUC access controls

Joshua Brindle and Mark Dilger

Discussion: https://postgr.es/m/47F87A0E-C0E5-43A6-89F6-D403F2B45175@enterprisedb.com

src/backend/utils/misc/guc.c

@@ -43,6 +43,7 @@
 #include "access/xlog_internal.h"
 #include "access/xlogrecovery.h"
 #include "catalog/namespace.h"
+#include "catalog/objectaccess.h"
 #include "catalog/pg_authid.h"
 #include "catalog/storage.h"
 #include "commands/async.h"
@@ -8736,6 +8737,18 @@ AlterSystemSetConfigFile(AlterSystemStmt *altersysstmt)
 		replace_auto_config_value(&head, &tail, name, value);
 	}
 
+	/*
+	 * Invoke the post-alter hook for altering this GUC variable.
+	 *
+	 * We do this here rather than at the end, because ALTER SYSTEM is not
+	 * transactional.  If the hook aborts our transaction, it will be cleaner
+	 * to do so before we touch any files.
+	 */
+	InvokeObjectPostAlterHookArgStr(InvalidOid, name,
+									ACL_ALTER_SYSTEM,
+									altersysstmt->setstmt->kind,
+									false);
+
 	/*
 	 * To ensure crash safety, first write the new file data to a temp file,
 	 * then atomically rename it into place.
@@ -8907,6 +8920,10 @@ ExecSetVariableStmt(VariableSetStmt *stmt, bool isTopLevel)
 			ResetAllOptions();
 			break;
 	}
+
+	/* Invoke the post-alter hook for setting this GUC variable. */
+	InvokeObjectPostAlterHookArgStr(InvalidOid, stmt->name,
+									ACL_SET_VALUE, stmt->kind, false);
 }
 
 /*