make pg_table_metadata CockroachDB compatible

CockroachDB doesn't support `index` as a table alias, but PostgreSQL
does. Since `idx` is supported by both, change the metadata query
accordingly.

Refs cockroachdb/cockroach#72407

server/src-rsr/pg_table_metadata.sql

@@ -59,28 +59,28 @@ LEFT JOIN LATERAL
       'constraint', jsonb_build_object('name', class.relname, 'oid', class.oid :: integer),
       'columns', coalesce(columns.info, '[]')
     ) AS info
-    FROM pg_catalog.pg_index index
+    FROM pg_catalog.pg_index idx
     JOIN pg_catalog.pg_class class
-      ON class.oid = index.indexrelid
+      ON class.oid = idx.indexrelid
     LEFT JOIN LATERAL
       ( SELECT jsonb_agg("column".attname) AS info
         FROM pg_catalog.pg_attribute "column"
         WHERE "column".attrelid = "table".oid
-          AND "column".attnum = ANY (index.indkey)
+          AND "column".attnum = ANY (idx.indkey)
       ) AS columns ON true
-    WHERE index.indrelid = "table".oid
-      AND index.indisprimary
+    WHERE idx.indrelid = "table".oid
+      AND idx.indisprimary
   ) primary_key ON true
 
 -- unique constraints
 LEFT JOIN LATERAL
   ( SELECT jsonb_agg(jsonb_build_object('name', class.relname, 'oid', class.oid :: integer)) AS info
-    FROM pg_catalog.pg_index index
+    FROM pg_catalog.pg_index idx
     JOIN pg_catalog.pg_class class
-      ON class.oid = index.indexrelid
-    WHERE index.indrelid = "table".oid
-      AND index.indisunique
-      AND NOT index.indisprimary
+      ON class.oid = idx.indexrelid
+    WHERE idx.indrelid = "table".oid
+      AND idx.indisunique
+      AND NOT idx.indisprimary
   ) unique_constraints ON true
 
 -- foreign keys