Add support for custom DISTRIBUTION metric

[macciomauro]

Enable DataDog distribution metric

This PR is copied from lexmag#54 but based on feature/switch_from_config branch

This feature unlock the possibility to have more specific metrics with percentiles calculations

⚠️ I think we need to think how to maintain this feature incrementing on Statix fork. I don't think we really wanna merge this PR on feature/switch_from_config branch ⚠️

The usage is the same of timing metrics

MyApp.Datadog.distribution(
          "my.metric.name",
          "123456789",
          tags: [ ]
        )

When the metric is displayed on DataDog we need to enable percentiles on Mentrics summary

[Rechyrex]

I had a look to the other PR and it looks good to me, but I do not have that much context on statix 👀 Probably better to wait for at least one other review

[macciomauro]

what can be the next steps to take it forward? more for the merge approach