Simple program to test telemetry and prometheus
> iex -S mix
> curl http://127.0.0.1:4000/
Hello World!
> curl http://127.0.0.1:4000/
Hello World!
> curl http://127.0.0.1:4000/metrics
# HELP http_request_payload_size
# TYPE http_request_payload_size counter
http_request_payload_size 99
# HELP http_request_count
# TYPE http_request_count counter
http_request_count 2