Refactor async proofing data storage

[mitchellhenke]

Previously, the async proofing process would store the arguments used for the vendor proofing call as backgrounds jobs were intended to load inputs from Redis instead of figuring out how to have the background job store encrypt its arguments. We use lambdas, so the storage of arguments isn't needed, and this refactor no longer stores the PII in redis.

There is a bit of complication to this because in the synchronous process the form data that gets submitted is sometimes used after the proofer vendor returns a response, and the redis-stored PII was kind of a stand-in for that. To work with that, the previous_..._params pattern was copied to save the user's input and then used as necessary after the vendor returns a successful response.

[zachmargolis]

Just did a first pass, but looks good! Will try to review more closely in a bit

[zachmargolis]

LGTM! Thanks for doing this