Find appointment vets-api client/service code

[kjduensing]

Issue Description

Context

The first thing vets-api needs to do to start a mileage submission is to find an appointment by appt date time for a user.

Impact

Doing this will allow us to kickoff the submission process.

Notes

• I'm not positive an endpoint exists on the TravelPay API to find an appointment by datetime, which may mean we need to get the ext appt id sooner rather than later
• This may change once we have direct access to the external (VistA or OracleHealth) appt ID - may just be able to pass that in

Endpoint Path

• Local: http://localhost:3000/travel_pay/v0/appointments?date=<appt_datetime>
• Staging: https://staging-api.va.gov/travel_pay/v0/appointments?date=<appt_datetime>
• Production: https://api.va.gov/travel_pay/v0/appointments?date=<appt_datetime>

Response Schema

{
  appointmentId: UUID
}

Back end tasks

• [ ] Client code written - calls correct endpoint
• [ ] Service code written - transforms/processes response from client
  • [ ] Handle errors
• [ ] ~Controller endpoint written~
• [ ] ~Config~
  • [ ] settings.test.yml updated if needed
  • [ ] settings.local.yml updated if needed
  • [ ] settings.yml updated if needed
  • [ ] infra-manifests updated if needed
  • [ ] dev
  • [ ] staging
  • [ ] prod
• [ ] Tests written
  • [ ] Unit
  • [ ] Happy path
  • [ ] Exhaustive failure paths
  • [ ] ~Integration~
  • [ ] ~VCR Cassettes~
  • [ ] ~Betamocks registration~
• [ ] Mock data
• [ ] Testing
  • [ ] Unit tests pass
  • [ ] ~QA testing - try to break it in staging~
• [ ] Improve 1 thing about the codebase
• [ ] ~Swagger docs updated~

Acceptance Criteria

• [ ] Backend tasks complete
• [ ] I can hit the endpoint defined above using postman or another testing tool and see the response defined above

[ayush-chak]

Hey team! Please add your planning poker estimate with Zenhub @hinzed1127 @kjduensing @liztownd