Assure that endpoints are up to date with IdP

[jgrevich]

Issue

As a login.gov load tester, I would like to make sure the fake server's endpoints are up-to-date with the IdP, So that I can load test the IAL2 flows that this codebase mocks.

Solution

• [ ] migrate Accuant endpoints to LN TrueID for doc auth
• [ ] add USPS IPP flows (https://github.com/18F/identity-fake-server/pull/24)
• [ ] add any other diffs between current IdP proofing endpoints and this repo to the issue

Acceptance Criteria

• [ ] sp_ial2 load tests complete without failure using this mock proofer.

[timothy-spencer]

A nice outcome from this issue would be that we know how to configure the idp so that it uses https://github.com/18F/identity-fake-server , which is deployed at https://fake-server.loadtest.identitysandbox.gov/