Model eligibility verification form field validation

[thekaveman]

Our current practice has been to offload input validation to the Eligibility Server, since we're simply a pass-through for rules and data defined there.

However this creates at least a couple potential issues:

• The user must submit their information before they know if it's formatted incorrectly, vs. immediate in-browser feedback
• The fields allow for any size and type of value, a potential DDoS vector

Given we will have more than one EligibilityVerifier in the next phase, each with unique form validation needs and UX considerations, now is the time to implement Eligibility verification form field validation.

Tasks

• Add a TextField or similar to the EligibilityVerifier model that captures a regex pattern that can be used to validate the sub field in the eligibility verification form.
• Add a PositiveIntegerField or similar to the EligibilityVerifier model that captures the maximum allowed length for the name field in the form.