Refactor Cloud Foundry metrics collection

[jsoriano]

Cloud Foundry metrics collection is implemented as push metricsets that obtain the metrics from the firehose. Current implementation has some problems:

• Each document created by these metricsets contain a single metric, with the metric name in a field, and the value in other. The approach used in Metricbeat is to store values in fields whose name is obtained from the name of the metric. This allows to store multiple related metrics in the same document.
• Metrics of different types are collected from different metricsets (counter and value), even when they are from the same services.

Create a single metricset that collects counters and values. Group metrics with the same dimensions in the same events.

[elasticmachine]

Pinging @elastic/integrations-platforms (Team:Platforms)

[botelastic]

Hi! We just realized that we haven't looked into this issue in a while. We're sorry! We're labeling this issue as Stale to make it hit our filters and make sure we get back to it as soon as possible. In the meantime, it'd be extremely helpful if you could take a look at it as well and confirm its relevance. A simple comment with a nice emoji will be enough :+1. Thank you for your contribution!