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.
