Add DisabilityDeterminationSourceType

Sourced from CEDS: https://ceds.ed.gov/CEDSElementDetails.aspx?TermId=8287

In the Disability Common type, add an optional element called DisabilityDeterminationSourceType of type DisabilityDeterminationSourceType.

Additionally, create a new Enumeration type called DisabilityDeterminationSourceType with the following enumeration values:
By physician
By health care provider
By school psychologist or other psychologist
By licensed physical therapist
Self-reported
By social service or other type of agency
Not applicable to the student
Unknown or Unreported
Other