Add optional text field for entering cause of death details

[hknahal]

Request from pancreatic cancer project to add an optional text field for entering details about cause of death if cause_of_death is Died of other reasons, or if patient died of a different cancer instead of the primary diagnosed cancer. Project explained that this is important in pancreatic cancer for censoring surgical deaths and treatment complications. This field would provide more granularity for the cause of death:

Field	Description	Data Tier	Attributes	Type
cause_of_death_details	Provide additional details regarding cause of death if donor.	Extended		Text

One option would be make this field required if cause_of_death = Died of other reasons.

[hknahal]

Follow up with Amber to find out if this field is still required