Exclude EXPLAIN queries from pg_stat_statements (#9358)

* postgres exclude EXPLAIN queries from pg_stat_statements

Update the collection of postgres query metrics to exclude `EXPLAIN` queries.

If deep database monitoring is enabled and we are collecting execution plans, then there will be at least one tracked EXPLAIN statement for every unique normalized query we encounter. Since these statements are not used in the product we exclude them from collection.

This updates postgres to have the same behavior as mysql, where we do the same exclusion for query metrics.

* escape

postgres/datadog_checks/postgres/statements.py

@@ -28,6 +28,7 @@
   LEFT JOIN pg_database
          ON pg_stat_statements.dbid = pg_database.oid
   WHERE query != '<insufficient privilege>'
+  AND query NOT LIKE 'EXPLAIN %%'
   {filters}
   LIMIT {limit}
 """