Updates to SSN Validation in Employee & Contractor Onboard Status

We have updated employee and contractor onboard status logic as it relates to SSN validation, removing the need to enter placeholder SSN values in order to run payroll. Previously, an employee or contractor needed a value in the SSN field or would have a `blocking` onboard status; SSN validation status was not considered in onboard status. Now, either a missing or invalid SSN will result in a `needs_attention` onboard status. This makes employee and contractor onboard statuses more comprehensive, making it simpler for you to surface missing or invalid SSNs to end users. These missing SSN values are important to resolve before tax filings. Read more about SSN validation and onboard status here.