Allow array fields on Patient to be empty

[gffking]

Due to the combination of how PatientUpdate is structured and how JSON serialization works in Go, it has not been possible to completely remove emails and phones from a Patient record.

This PR updates PatientUpdate so that if Emails or Phones is non-nil, the field will be included in the JSON serialization output, even if the slice the field points to is empty. This allows consumers of the client to pass an empty array for these fields to Elation to allow them to be completely cleared.

If Emails or Phones is nil, then it will not be included in the JSON serialization output. This allows consumers of the client to change other fields on the Patient record without affecting emails or phones.

For consistency, the Consents and Insurances fields have been similarly modified to allow the fields in the Patient record to be cleared.