### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

When a scheduled rules runs, an empty event is generated and sent to targets.

### Expected Behavior

An event like this sample should be sent.
```json
{
  "version": "0",
  "id": "89d1a02d-5ec7-412e-82f5-13505f849b41",
  "detail-type": "Scheduled Event",
  "source": "aws.events",
  "account": "123456789012",
  "time": "2016-12-30T18:44:49Z",
  "region": "us-east-1",
  "resources": ["arn:aws:events:us-east-1:123456789012:rule/SampleRule"],
  "detail": {}
}
```

### How are you starting LocalStack?

With a docker-compose file

### Steps To Reproduce

#### How are you starting localstack (e.g., `bin/localstack` command, arguments, or `docker-compose.yml`)

    docker-compose up

#### Client commands (e.g., AWS SDK code snippet, or sequence of "awslocal" commands)

    awslocal events put-rule --name scheduled_rule --schedule-expression "rate(1 minutes)"
    awslocal events put-targets --rule scheduled_rule --targets "Id"="1","Arn"="arn:aws:logs:us-east-1:000000000000:log-group:/aws/events/echo"
    awslocal--endpoint-url=http://localhost:4566 logs tail "/aws/events/echo"

### Environment

```markdown
- OS: macOS Monterey
- LocalStack: 0.13.3
```


### Anything else?
I think [this](https://github.com/localstack/localstack/blob/1567f25a8f672f4dec23cb7cb1aadb5a744366f8/localstack/services/events/events_listener.py#L92) means an non-empty event is sent only when an input is `Constant (JSON text)`.
![image](https://user-images.githubusercontent.com/4127030/151643813-a4d1e113-dba3-41ad-8400-da57e4f674a1.png)

input_path = target.get("InputPath")
    if input_path:
        event = extract_jsonpath(event, input_path)
    return event
def process_events(event: Dict, targets: List[Dict]):
    for target in targets:
        arn = target["Arn"]
        changed_event = filter_event_with_target_input_path(target, event)
        if target.get("Input"):
            changed_event = json.loads(target.get("Input"))
        try:
            send_event_to_target(
                arn,
                changed_event,
                pick_attributes(target, ["$.SqsParameters", "$.KinesisParameters"]),
                role=target.get("RoleArn"),
                target=target,
                source_service=ServicePrincipal.events,
                source_arn=target.get("RuleArn"),
            )
        except Exception as e:
            LOG.info(f"Unable to send event notification {truncate(event)} to target {target}: {e}")
def get_event_bus_name(event_bus_name_or_arn: Optional[EventBusNameOrArn] = None) -> str:
    event_bus_name_or_arn = event_bus_name_or_arn or DEFAULT_EVENT_BUS_NAME
    return event_bus_name_or_arn.split("/")[-1]
def events_handler_put_events(self):
    entries = self._get_param("Entries")