Correct inner join to use proper aliases (#1978)

"_" was used for all the internal json_agg aliases. Now an alias
with "_" plus a local table name is used.

Co-authored-by: Cole Arendt <cole.arendt@outlook.com>

test/fixtures/privileges.sql

@@ -156,6 +156,9 @@ GRANT ALL ON TABLE
     , products_suppliers
     , trade_unions
     , suppliers_trade_unions
+    , client
+    , clientinfo
+    , contact
 TO postgrest_test_anonymous;
 
 GRANT INSERT ON TABLE insertonly TO postgrest_test_anonymous;