fix: also fix metadata loading issue for PG 16

add: meta_data.sql for PG16

backend/sql/16/meta_data.sql

@@ -0,0 +1,13 @@
+SELECT * FROM (
+        SELECT c.relname AS label, n.oid as namespace_id, c.reltuples AS cnt
+        FROM pg_catalog.pg_class c
+        JOIN pg_catalog.pg_namespace n
+        ON n.oid = c.relnamespace
+        WHERE c.relkind = 'r'
+        AND n.nspname = '%s'
+) as q1
+JOIN ag_graph as g ON q1.namespace_id = g.namespace
+INNER JOIN ag_label as label
+
+ON label.name = q1.label
+AND label.graph = g.graphid;