Validate 21a addresses

[gabezurita]

ARM's Find a Rep (FAR) uses LH address validation before displaying Google Maps links to Representatives for 2122 requests. They do not display invalid addresses.

Given GCLAWS will not implement address validation until a few more quarters (per their estimate), it would be good to validate addresses on the vets-api side before sending them to the GCLAWS API.

AC

• [ ] Using the FAR implementation as an example, hit the LH API to validate 21a representative-applicant addresses
• [ ] Surface a user error if the input address is not valid (will require design/product feedback)

[holdenhinkle]

ARM Address validation using the Lighthouse Address Validation API - https://github.com/department-of-veterans-affairs/vets-api/blob/master/modules/veteran/app/sidekiq/representatives/update.rb#L39