[Feature Request] Expose build metrics as prometheus or other formats

[jamil-s]

From a infrastructure maintainer, it would be beneficial to get insights into the operations of Kaniko. Some metrics that would be helpful in fine-tuning build processes would be

• Cache hit/miss
• snapshot size
• Build duration

For starters these would be great if we can find a way to expose them as prometheus metrics or statsd or some other accepted format