### 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)

"version": "0",
            "id": event_envelope["uuid"],
            "detail-type": event.get("DetailType"),
            "source": event.get("Source"),
            "account": self.current_account,
            "time": event_time.strftime("%Y-%m-%dT%H:%M:%SZ"),
            "region": self.region,
            "resources": event.get("Resources", []),
            "detail": json.loads(event.get("Detail", "{}")),
        }
        targets = []
        for rule in matching_rules:
            if filter_event_based_on_event_format(self, rule.name, event_bus_name, formatted_event):
                rule_targets = self.events_backend.list_targets_by_rule(
                    rule.name, event_bus_arn(event_bus_name)
                ).get("Targets", [])
                targets.extend([{"RuleArn": rule.arn} | target for target in rule_targets])
        
        process_events(formatted_event, targets)
    content = {
        "FailedEntryCount": 0,  
        "Entries": list(map(lambda event: {"EventId": event["uuid"]}, events)),
    }
    self.response_headers.update(
        {"Content-Type": APPLICATION_AMZ_JSON_1_1, "x-amzn-RequestId": short_uid()}
    )
    return json.dumps(content), self.response_headers
def apply_patches():
    MotoEventsHandler.put_events = events_handler_put_events