Add /health endpoint

[zacdezgeo]

Problem Description

To verify if the API is running, an end-user must either hit the /get_fields or the /summary endpoints. It'd be better practice to have a dedicated endpoint for verifying the status of the API.

Expected behavior

I'd like to verify that the API is up and running by hitting the /health endpoint:

curl -X GET "http://localhost:8000/health"

Expected response:

{
  "status": "ok"
}