### 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)

self,
        context: RequestContext,
        rule: RuleName,
        targets: TargetList,
        event_bus_name: EventBusNameOrArn = None,
    ) -> PutTargetsResponse:
        validation_errors = []
        id_regex = re.compile(r"^[\.\-_A-Za-z0-9]+$")
        for index, target in enumerate(targets):
            id = target.get("Id")
            if not id_regex.match(id):
                validation_errors.append(
                    f"Value '{id}' at 'targets.{index + 1}.member.id' failed to satisfy constraint: Member must satisfy regular expression pattern: [\\.\\-_A-Za-z0-9]+"
                )
            if len(id) > 64:
                validation_errors.append(
                    f"Value '{id}' at 'targets.{index + 1}.member.id' failed to satisfy constraint: Member must have length less than or equal to 64"
                )
        if validation_errors:
            errors_message = "; ".join(validation_errors)
            message = f"{len(validation_errors)} validation {'errors' if len(validation_errors) > 1 else 'error'} detected: {errors_message}"
            raise CommonServiceException(message=message, code="ValidationException")
        return call_moto(context)
def _get_events_tmp_dir():