fix: Update instrumentation pg to support merge statements (#1317)

* fix: support merge statement in pg versions 15+

* chore: fix json formatting for pg fixtures

* chore: use aliases in pg fixtures table for merge statement

instrumentation/pg/lib/opentelemetry/instrumentation/pg/constants.rb

@@ -40,10 +40,10 @@ module Constants
           LISTEN
           LOAD
           LOCK
+          MERGE
           MOVE
           NOTIFY
           PREPARE
-          PREPARE
           REASSIGN
           REFRESH
           REINDEX
@@ -54,7 +54,6 @@ module Constants
           SAVEPOINT
           SECURITY
           SELECT
-          SELECT
           SET
           SHOW
           START

instrumentation/pg/test/fixtures/sql_table_name.json

@@ -54,5 +54,9 @@
     {
       "name": "table_name_with_double_quotes",
       "sql": "SELECT columns FROM \"test_table\""
+    },
+    {
+      "name": "merge",
+      "sql": "MERGE INTO test_table AS t USING other_table AS o ON (o.id = t.id) WHEN MATCHED THEN UPDATE SET x = t.x + 1 WHEN NOT MATCHED THEN INSERT (id, x, status) VALUES (o.id, o.x, o.status)"
     }
 ]