feat: add configurable timezone for Snowflake table export

Add `timezone` API parameter to `POST /v2/storage/tables/{table_id}/export-async`
endpoint (Snowflake only). When set, the Exporter configures Snowflake session
timezone before COPY INTO, affecting TIMESTAMP_LTZ column display in exports.

Flows through ExportTableRequest -> TableExportOptions -> Snowflake backend ->
db-import-export ExportOptions which already supports timezone (v4.4.0).

Author: zajca

apiary.apib

@@ -3415,6 +3415,7 @@ will show information about the created file and caching:
             + csv - CSV file
             + parquet - Parquet file
         + Default: csv
+    + timezone (optional, string) - IANA timezone name (e.g. `America/Los_Angeles`, `Europe/Prague`). When set, Snowflake session timezone is configured before export, affecting TIMESTAMP_LTZ column display. Not supported for Parquet exports. Available only for Snowflake backend.
 
 + Request (application/json)
     + Headers
@@ -3443,6 +3444,7 @@ will show information about the created file and caching:
                         "format": "rfc",
                         "whereFilters": [],
                         "fileType": "csv",
+                        "timezone": null
                     },
                     "queue": "main_fast"
                 },

src/Keboola/StorageApi/Client.php

@@ -1771,6 +1771,7 @@ private function prepareExportOptions(array $options)
             'fulltextSearch',
             'includeInternalTimestamp',
             'fileType',
+            'timezone',
         ];
 
         $filteredOptions = array_intersect_key($options, array_flip($allowedOptions));