SupplierFramework model: make prefill_declaration_from_supplier_framework relationship viewonly
SupplierFramework model: make prefill_declaration_from_supplier_framework relationship viewonly

this should silence a warning from sqlalchemy about a collision of multiple
relationships being able to write to supplier_id - we probably don't want
people being able to inadvertantly flip the supplier_id through setting
prefill_declaration_from_supplier_framework anyway

alphagov/digitalmarketplace-api,alphagov/digitalmarketplace-api,alphagov/digitalmarketplace-api