accounts,customers: sdn_type is invalid database type

[adamdecaf]

Customers Version: v0.6.0

The sdn_type on account and customer OFAC storage results is an integer when it should be a string.

• https://github.com/moov-io/customers/blob/master/migrations/006_create_customer_ofac_searches.up.sql#L5
• https://github.com/moov-io/customers/blob/master/migrations/014_create_account_ofac_searches.up.sql#L6