Improve error messages when invalid requested_core_field exception submitted.

[edsu7]

The error message provided for a non-existent requested_core_field is the same as an invalid/non-eligible requested_core_field (e.g. ID) field in the https://clinical.qa.argo.cancercollaboratory.org/exception/TEST-GR/entity API.

Detailed Description

Non-existent field TSV:

program_name	submitter_donor_id	submitter_specimen_id	schema	requested_core_field	requested_exception_value
TEST-GR	TEST-DONOR_1	TEST-SPECIMEN_1	specimen	relapse_type	Unknown

API response:

"The requested_core_field 'relapse_type' does not match schema 'specimen'. Please update your exception request form."

ID field

program_name	submitter_donor_id	submitter_specimen_id	schema	requested_core_field	requested_exception_value
TEST-GR	TEST-DONOR_1	TEST-SPECIMEN_1	specimen	submitter_primary_diagnosis_id	Unknown

API response

"The requested_core_field 'submitter_primary_diagnosis_id' does not match schema 'specimen'. Please update your exception request form."

Possible Implementation

For the later, the API response could be:

"The requested_core_field 'submitter_primary_diagnosis_id' in schema 'specimen' is not eligible for exception. Please update your exception request form."