Add metrics for failed liveness checks

[plamen-bardarov]

• Read the Contributing document.

Summary

The proposed change is to improve the observability of failed Liveness Checks by emitting a metric.
cloudfoundry/diego-release#953

Backward Compatibility

Breaking Change? No

[linux-foundation-easycla]

The committers listed above are authorized under a signed CLA.

• ✅ login: plamen-bardarov / name: Plamen Bardarov (060c6b1, fd0b20c)

[ameowlia]

👋 Hi @plamen-bardarov and @vlast3k,

Apologizes for the delay in the review. We have been struggling to get the Diego pipeline green, it is sadly still not green.

✅ The code looks good.
✅ I ran this IRL and was able to see the expected output.
❓ Can you please add a bosh level property to turn off this value by default?
😢 The pipeline is not green.

Once you get the config property in I will approve. And then once the pipeline is green I will merge.

[plamen-bardarov]

Hi @ameowlia, do you mean adding 1 property to enable sending liveness check failure metrics altogether or you mean introducing more granular control over which types of liveness/startup check failures to emit(HTTP/TCP/etc.)?

[plamen-bardarov]

Added new property for enabling the metrics. Will also create PR for diego-release
Update: Heres the PR for diego-release cloudfoundry/diego-release#964