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.

script/test/fixtures/v3/output-k8s-full-example.json

@@ -197,6 +197,16 @@
                 "mountPath": "/tmp"
               }
             ],
+            "livenessProbe": {
+              "exec": {
+                "command": [
+                  "echo \"hello world\""
+                ]
+              },
+              "timeoutSeconds": 1,
+              "periodSeconds": 10,
+              "failureThreshold": 5
+            },
             "securityContext": {
               "capabilities": {
                 "add": [

script/test/fixtures/v3/output-os-full-example.json

@@ -197,6 +197,16 @@
                 "mountPath": "/tmp"
               }
             ],
+            "livenessProbe": {
+              "exec": {
+                "command": [
+                  "echo \"hello world\""
+                ]
+              },
+              "timeoutSeconds": 1,
+              "periodSeconds": 10,
+              "failureThreshold": 5
+            },
             "securityContext": {
               "capabilities": {
                 "add": [