Search for open appt slots at OH facility

[bcrosbyva]

To facilitate the searching for open appointment slots at Oracle Health facilities, a new VetsAPI endpoint must be created in the vaos module to route the appropriate request to VetsAPI Patient Gateway (VPG).

• endpoint should be GET '/locations/:location_id/slots'
• either clinicIEN or clinicalServiceId must be supplied as query parameters
  • a HTTP 400 error if neither is provided
• start_dt and end_dt are also required datetime parameters
• requests are sent to the /vpg/v1/slots endpoint being developed with CES-220