Add custom "alive-endpoint" in config section / CLI for HTTP monitoring

* Support for custom alive endpoint in CLI / .dropstack.json

**Example**

```bash
dropstack deploy --alive-endpoint /info
```

```json
{
  "variables": [],
  "instances": 1,
  "type": "mono",
  "name": "foo",
  "serviceUrl": "foo.cloud.dropstack.run",
  "aliveEndpoint": "/info"
}
```