This update enhances the system's ability to access information related to signed documents (o2m relationships). Previously, limitations prevented developers from leveraging these relationships, now they can be customized, allowing for more comprehensive sign management. This improves the flexibility and functionality of our sign workflows.

The class `SignerX2Many` is inheritable, but if we need another value from the o2m, we can't use it because the `signerX2Many` is not exportable.

Enable `signerX2Many` customization, allowing more fields to be read from the `sign.send.request.signer` model.