Add debug events to notify of debugging containers started and terminated

[briandealwis]

Relates to #3122
Fixes #2211

Description

Implements two events to notify of a debugging container being started and terminated. Also exposes a list of currently running debugging containers via the Skaffold state object. The IDEs can monitor for events to populate UIs.

`/v1/events` stream of `skaffold debug` within `examples/jib`

In this example, we do a skaffold debug, and then kill the deployed pod. The deployment starts a new pod. We get a terminated event for the container for the killed pod.

{
  "result": {
    "timestamp": "2019-11-27T21:24:55.264570Z",
    "event": {
      "buildEvent": {
        "artifact": "gcr.io/k8s-skaffold/skaffold-jib",
        "status": "In Progress"
      }
    },
    "entry": "Build started for artifact gcr.io/k8s-skaffold/skaffold-jib"
  }
}
{
  "result": {
    "timestamp": "2019-11-27T21:24:57.984646Z",
    "event": {
      "buildEvent": {
        "artifact": "gcr.io/k8s-skaffold/skaffold-jib",
        "status": "Complete"
      }
    },
    "entry": "Build completed for artifact gcr.io/k8s-skaffold/skaffold-jib"
  }
}
{
  "result": {
    "timestamp": "2019-11-27T21:24:57.989845Z",
    "event": {
      "deployEvent": {
        "status": "In Progress"
      }
    },
    "entry": "Deploy started"
  }
}
{
  "result": {
    "timestamp": "2019-11-27T21:24:59.423482Z",
    "event": {
      "deployEvent": {
        "status": "Complete"
      }
    },
    "entry": "Deploy complete"
  }
}
{
  "result": {
    "timestamp": "2019-11-27T21:25:01.828798Z",
    "event": {
      "debuggingContainerEvent": {
        "status": "Started",
        "podName": "web-6c684c7d47-2xzxd",
        "containerName": "web",
        "namespace": "default",
        "artifactImage": "gcr.io/k8s-skaffold/skaffold-jib",
        "runtime": "jvm",
        "ports": {
          "jdwp": 5005
        }
      }
    },
    "entry": "Debuggable container started pod/web-6c684c7d47-2xzxd:web (default)"
  }
}
{
  "result": {
    "timestamp": "2019-11-27T21:25:50.806149Z",
    "event": {
      "debuggingContainerEvent": {
        "status": "Started",
        "podName": "web-6c684c7d47-66lct",
        "containerName": "web",
        "namespace": "default",
        "artifactImage": "gcr.io/k8s-skaffold/skaffold-jib",
        "runtime": "jvm",
        "ports": {
          "jdwp": 5005
        }
      }
    },
    "entry": "Debuggable container started pod/web-6c684c7d47-66lct:web (default)"
  }
}
{
  "result": {
    "timestamp": "2019-11-27T21:25:50.819426Z",
    "event": {
      "debuggingContainerEvent": {
        "status": "Terminated",
        "podName": "web-6c684c7d47-2xzxd",
        "containerName": "web",
        "namespace": "default",
        "artifactImage": "gcr.io/k8s-skaffold/skaffold-jib",
        "runtime": "jvm",
        "ports": {
          "jdwp": 5005
        }
      }
    },
    "entry": "Debuggable container terminated pod/web-6c684c7d47-2xzxd:web (default)"
  }
}

The `/v1/state` listing debugging containers

{
  "buildState": {
    "artifacts": {
      "gcr.io/k8s-skaffold/skaffold-jib": "Complete"
    }
  },
  "deployState": {
    "status": "Complete"
  },
  "statusCheckState": {
    "status": "Not Started"
  },
  "fileSyncState": {
    "status": "Not Started"
  },
  "debuggingContainers": [
    {
      "status": "Started",
      "podName": "web-6c684c7d47-66lct",
      "containerName": "web",
      "namespace": "default",
      "artifactImage": "gcr.io/k8s-skaffold/skaffold-jib",
      "runtime": "jvm",
      "ports": {
        "jdwp": 5005
      }
    }
  ]
}

User facing changes

n/a

Submitter Checklist

These are the criteria that every PR should meet, please check them off as you
review them:

• Includes unit tests
• Mentions any output changes.
• Adds documentation as needed: user docs, YAML reference, CLI reference.
• Adds integration tests if needed.

Reviewer Notes

• The code flow looks good.
• Unit test added.
• User facing changes look good.

Release Notes

n/a — for internal consumption

[codecov]

Codecov Report

Merging #3312 into master will decrease coverage by 0.12%.
The diff coverage is 67.34%.

Impacted Files	Coverage Δ
pkg/skaffold/runner/runner.go	0% <ø> (ø)	⬆️
pkg/skaffold/config/options.go	100% <ø> (ø)	⬆️
pkg/skaffold/runner/debugging.go	0% <0%> (ø)
pkg/skaffold/debug/debug.go	41.93% <0%> (-1.4%)	⬇️
cmd/skaffold/app/cmd/debug.go	46.15% <0%> (-3.85%)	⬇️
pkg/skaffold/runner/dev.go	64.6% <0%> (-2.38%)	⬇️
pkg/skaffold/debug/transform_jvm.go	94.73% <100%> (ø)	⬆️
pkg/skaffold/debug/transform_python.go	85.05% <100%> (ø)	⬆️
pkg/skaffold/debug/transform_nodejs.go	78.64% <100%> (ø)	⬆️
pkg/skaffold/debug/transform_go.go	86.17% <100%> (ø)	⬆️
... and 5 more

[briandealwis]

PTAL @quoctruong

[briandealwis]

@etanshaul too

[briandealwis]

Closing. Will re-open as smaller pieces.