Create Org API endpoint must return better error for duplicate names

[Cynthia Kiser]

We need to put a try/except around saving the org and then return sensible error messages in JSON format.

Example of an error we need to catch and report:

IntegrityError at /api/organizations/
duplicate key value violates unique constraint "data_organization_name_key"
DETAIL:  Key (name)=(test org 2) already exists.
Request Method:	POST
Request URL:	http://localhost:8888/api/organizations/
Django Version:	3.1.8
Exception Type:	IntegrityError
Exception Value:	
duplicate key value violates unique constraint "data_organization_name_key"
DETAIL:  Key (name)=(test org 2) already exists.