Refactor usage of json parser expresss middleware, see https://github.com/18F/federalist/pull/3510

[amirbey]

User Story

Background (Optional)

The JSON parser express middleware should not happen until the request is validated and authorized.

Acceptance Criteria

• [ ] refactor handling of requests to ensure they are only parsed when necessary
• [ ] Change made live via Federalist

After evaluating, edit this part:

Level of effort - <low/medium/high>

Implementation outline (if higher than "low" effort):

• [ ] <TODO>