Introduce 'status' label into metrics

[jochbru]

The Pingdom API has a 'status' property, enabling visibility of the current status of a check. This could include statuses such as "up", "down", "unconfirmed_down", "unknown", "paused".

We encountered a problem with the metrics wherein a check, after being paused, would transition to 'unknown' status. Because this status does not explicitly indicate that the check is 'up', the 'pingdom_uptime_status' metrics would return a 0 value, without any possibility to discern the specific reason for this value.

Please see this snippet of code for a deeper understanding:

pingdom-exporter/cmd/pingdom-exporter/main.go

Lines 153 to 159 in 24526d5

	var status float64
	paused := "false"
	if check.Status == "paused" {
	paused = "true"
	} else if check.Status == "up" {
	status = 1
	}

In response, this Pull Request (PR) introduces a 'status' label into the following metrics:

• pingdom_uptime_status
• pingdom_uptime_response_time_seconds

As this label mirrors the value from the Pingdom API, it equips us with the ability to further filter out checks in the 'unconfirmed_down' or 'unknown' states, which would otherwise return a 0 value, without affecting the default behavior of existing implementations.

[jochbru]

@danielfm did you have a chance to review this PR?

[danielfm]

This is a good contribution, thanks. Sorry for the delay.