now works with a saved metric via settings svc

[dcosgrove]

NOTE: an image created from this branch has already been built and pushed to:
quay.io/paperlesspost/hpa-example:configurable-metric

Instructions for use on earth

1. Generate an authentication token (might need to be refreshed every 5~ minutes)

export AUTH_TOKEN="$(curl -d '{"email_address" : "dcosgrove@paperlesspost.com", "password" : "Stampy"}' https://earth.ppstaging.net/flyer/api/auth/login |jq -r '.data.id_token' -)"

2. Change example_metric (you can change this value from 10 to whatever you want)

curl -X PUT -H "Content-Type: application/json" -H "Authorization: Bearer $AUTH_TOKEN" -d '{"settings": { "example_metric": { "value": 10 }}}' https://earth.ppstaging.net/flyer/api/settings/hpa-example
Get the metric via hpa-example pods running on earth

Sample response

Sample metrics response from `/metrics':

$ curl localhost:8000/metrics            
# HELP example_metric Custom arbitrary value to test example HPA
# TYPE example_metric gauge
example_metric 10