Add field_options parameter(optional) in the respective functions in signature requests

[dev-jey]

Description

1. Add field options parameter(optional) in all functions updated in the respective api calls
   • Add field options parameter(optional) in the _send_signature_request function
   • Add field options parameter(optional) in the _create_unclaimed_draft function
2. This should solve issue No way to set field_options in signature requests. #90

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[jtreminio-dropbox]

Please use the new OpenAPI SDK: https://pypi.org/project/dropbox-sign/