feat(snowflake): Transpile exp.DatetimeAdd (#4349)

Author: VaggelisD

sqlglot/dialects/snowflake.py

@@ -786,6 +786,7 @@ class Generator(generator.Generator):
             exp.Create: transforms.preprocess([_flatten_structured_types_unless_iceberg]),
             exp.DateAdd: date_delta_sql("DATEADD"),
             exp.DateDiff: date_delta_sql("DATEDIFF"),
+            exp.DatetimeAdd: date_delta_sql("TIMESTAMPADD"),
             exp.DatetimeDiff: timestampdiff_sql,
             exp.DateStrToDate: datestrtodate_sql,
             exp.DayOfMonth: rename_func("DAYOFMONTH"),

tests/dialects/test_bigquery.py

@@ -656,6 +656,7 @@ def test_bigquery(self):
                     "bigquery": "SELECT DATETIME_ADD('2023-01-01T00:00:00', INTERVAL '1' MILLISECOND)",
                     "databricks": "SELECT TIMESTAMPADD(MILLISECOND, '1', '2023-01-01T00:00:00')",
                     "duckdb": "SELECT CAST('2023-01-01T00:00:00' AS DATETIME) + INTERVAL '1' MILLISECOND",
+                    "snowflake": "SELECT TIMESTAMPADD(MILLISECOND, '1', '2023-01-01T00:00:00')",
                 },
             ),
         )