Provide insights on when a metric was scraped for the last time

[tomkerkhove]

Provide insights on when a metric was scraped for the last time.

According to the Exposition format you can provide that as part of the information:

metric_name [
  "{" label_name "=" `"` label_value `"` { "," label_name "=" `"` label_value `"` } [ "," ] "}"
] value [ timestamp ]

However, this is not supported yet in Prometheus.Client so we're seeing if that's possible. (prom-client-net/prom-client#18)

The alternative is to add this to the description via a suffix - (<stamp>)

Related to #198

[tomkerkhove]

This is done via #285