Allow Shopify integrations to use processed_at as the Order Date (or map it as a custom field)

We recently migrated thousands of active, unfulfilled orders from another e-commerce platform to Shopify. Shopify correctly preserves the original purchase date in the processed_at field while the created_at field reflects the date the order was imported into Shopify.

Currently, ShipStation always uses Shopify's created_at field as the Order Date, and there is no option to instead use processed_at or map it as a custom field.

This creates a significant operational issue for merchants fulfilling migrated orders because the Order Date shown in ShipStation is the migration date rather than the customer's actual purchase date.

This is not an issue with Shopify preserving the data—the original purchase date is still available in Shopify via processed_at. The limitation is that ShipStation currently only reads created_at, with no configuration option to use another Shopify timestamp.

It would be extremely helpful if ShipStation could support one of the following:

1. Allow merchants to choose whether Shopify Order Date is sourced from created_at or processed_at.
2. Expose processed_at as a Custom Field Mapping option.
3. Provide an alternate sortable/displayable field in ShipStation that uses Shopify's processed_at.

Supporting one of these options would make ShipStation much more migration-friendly for Shopify merchants while maintaining the current default behavior for existing stores.