Adds healthcheck

This PR adds support for HealthCheck, being able to supply, for example:

```yaml
version: "3"

services:
  redis:
    image: redis
    healthcheck:
      test: echo "hello world"
      interval: 10s
      timeout: 1s
      retries: 5
```

Which is then converted to:

```yaml
spec:
  containers:
  - image: redis
    livenessProbe:
      exec:
        command:
        - echo "hello world"
      failureThreshold: 5
      periodSeconds: 10
      timeoutSeconds: 1
    name: redis
    resources: {}
  restartPolicy: Always
```

At the moment, this only supports livenessProbe, with support for readinessProbe in the future.

pkg/kobject/kobject.go

@@ -99,8 +99,20 @@ type ServiceConfig struct {
 	Dockerfile      string              `compose:"dockerfile"`
 	Replicas        int                 `compose:"replicas"`
 	GroupAdd        []int64             `compose:"group_add"`
-	// Volumes is a struct which contains all information about each volume
-	Volumes []Volumes `compose:""`
+	Volumes         []Volumes           `compose:""`
+	HealthChecks    HealthCheck         `compose:""`
+}
+
+// HealthCheck the healthcheck configuration for a service
+// "StartPeriod" is not yet added to compose, see:
+// https://github.com/docker/cli/issues/116
+type HealthCheck struct {
+	Test        []string
+	Timeout     int32
+	Interval    int32
+	Retries     int32
+	StartPeriod int32
+	Disable     bool
 }
 
 // EnvVar holds the environment variable struct of a container