[Eng] Update validation language for SSN input

[nichole-aquino]

Reference

Design ticket: #389

Overview:

• Update the error UI to reflect USWDS
• Allow users to input the SSN with or without dashes
• Provide a general error message "Enter a valid Social Security number" for all client-side validation. Here is our rationale:

1. If there are multiple errors, the error message would get quite long and outweigh the benefit of identifying where exactly an error occurred (in a likely instance, someone may have just entered a typo or was mistaken about what the SSN is). A long message, for example, would be:

Social Security Number must have a valid set of digits at the beginning (not 9, 666, or 000), a valid set of digits in the middle (not 00), and a valid set of digits at the end (not 0000).

2. There isn't any existing documentation on error state variants for SSN, so this would warrant further research to understand the use case better and test, if needed, the most appropriate copy.

AC

The changes should apply to the following error types:

• Invalid set of digits in all locations.
• Invalid set of digits at the beginning.
• Invalid set of digits in the middle.
• Invalid set of digits at the end.
• Invalid set of digits in the middle and end.
• Invalid amount of digits.