[#159173326] Output metrics /w Prom exposition fmt
[#159173326] Output metrics /w Prom exposition fmt

Change the Prometheus metrics exporter to include TYPE annotations.

See https://github.com/alphagov/paas-log-cache-adapter/pull/4

alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf,alphagov/paas-cf