Create Prometheus Data Model

[adamgfraser]

We want ZIO ZMX to support Promtheus as well as statd. We currently support a version of this today, see the PrometheusSpec.scala file in the test folder, but it relies on a dependency on the Prometheus client which we do not want to have. Therefore, we need to do our own implementation of the Prometheus protocol.

The first step to do this is to create a data model for the objects within the Prometheus data model, for example the Counter, Histogram, and CollectorRegistry. At this point this would be a pure data model that would describe the information we would need to interact with Prometheus but would not contain any of the actual logic for converting this data into the format expected by Prometheus.

[atooni]

Apart from working on ticket zio/zio#4384 I would like to give this a go in the hackathon.

[toxicafunk]

The model needs to able to output the write004 TextFormat which is what the Prometheus Server interprets in order to create its graphs.

[adamgfraser]

@atooni Great!

[atooni]

Specification of the text format : https://prometheus.io/docs/instrumenting/exposition_formats/

[atooni]

I propose to close this as the PR has been merged