feat: Added the product_id_base64_url_encoded field to InsertProductInputRequest, DeleteProductInputRequest, and GetProductRequest. This allows for product IDs containing special characters to be correctly handled when unpadded base64url-encoded

feat: Added several fields to enhance shipping configurations:
    - `handling_cutoff_time` and `handling_cutoff_timezone` within the `Shipping` message
    - `ShippingBusinessDaysConfig` message to define business days for shipping
    - `shipping_handling_business_days` and `shipping_transit_business_days` in `ProductAttributes`
    - `HandlingCutoffTime` message to configure country-specific handling cutoffs
    - `handling_cutoff_times` array in `ProductAttributes`
docs: Updated various comments, including links to data source creation guides

PiperOrigin-RevId: 830818193

Source-Link: googleapis/googleapis@659ea6e

Source-Link: googleapis/googleapis-gen@958d93e
Copy-Tag: eyJwIjoiU2hvcHBpbmdNZXJjaGFudFByb2R1Y3RzLy5Pd2xCb3QueWFtbCIsImgiOiI5NThkOTNlYjFmODIyOWRmZmM4ZmExYjljNGQ2MWY0ZjBhMWNmNDhkIn0=

Author: gcf-owl-bot[bot]