feat: add action duration metric

[Trojan295]

This PR adds the following metrics:

• action_started_total - count of started actions by type
• action_executed_duration_seconds - summary metric of the action duration for quantiles 0.5, 0.9 and 0.99.

It also adds support to export histogram and summary type metrics.

For action_executed_duration_seconds I decided to use a summary instead of a histogram to limit the number of series we send. Our action duration can range from milliseconds to dozens of seconds, so we might need up to 16 buckets to have some good data (and the _count, _sum series). If we want to have action type as dimension (we have 14 of those), that means:
3k clusters * 2 pods * (16 + 2) series * 14 action types = 1 512 000 series.

With a summary for 3 quantiles, we get:
3k clusters * 2 pods * (3 + 2) series * 14 action types = 420 000 series.

Still a lot, so we might consider keeping the metric export disabled by default and enable via env var (or maybe remotely from Cast AI).
Another drawback with summaries vs histograms is that we cannot aggregate them, because of the precalculation done on client side.