Add grantable MAINTAIN privilege and pg_maintain role.

Allows VACUUM, ANALYZE, REINDEX, REFRESH MATERIALIZED VIEW, CLUSTER,
and LOCK TABLE.

Effectively reverts 4441fc704d. Instead of creating separate
privileges for VACUUM, ANALYZE, and other maintenance commands, group
them together under a single MAINTAIN privilege.

Author: Nathan Bossart
Discussion: https://postgr.es/m/20221212210136.GA449764@nathanxps13
Discussion: https://postgr.es/m/45224.1670476523@sss.pgh.pa.us

src/backend/commands/lockcmds.c

@@ -300,6 +300,9 @@ LockTableAclCheck(Oid reloid, LOCKMODE lockmode, Oid userid)
 	else
 		aclmask = ACL_UPDATE | ACL_DELETE | ACL_TRUNCATE;
 
+	/* MAINTAIN privilege allows all lock modes */
+	aclmask |= ACL_MAINTAIN;
+
 	aclresult = pg_class_aclcheck(reloid, userid, aclmask);
 
 	return aclresult;