### 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)

if config.is_local_test_mode():
        TEST_EVENTS_CACHE.extend(entries)
    events = list(map(lambda event: {"event": event, "uuid": str(long_uid())}, entries))
    _dump_events_to_files(events)
    for event_envelope in events:
        event = event_envelope["event"]
        event_bus_name = get_event_bus_name(event.get("EventBusName"))
        event_bus = self.events_backend.event_buses.get(event_bus_name)
        if not event_bus:
            continue
        matching_rules = [
            r
            for r in event_bus.rules.values()
            if r.event_bus_name == event_bus_name and not r.scheduled_expression
        ]
        if not matching_rules:
            continue
        event_time = datetime.datetime.utcnow()
        if event_timestamp := event.get("Time"):
            try:
                
                event_time = datetime.datetime.utcfromtimestamp(event_timestamp)
            except ValueError:
                
                LOG.debug(
                    "Could not parse the `Time` parameter, falling back to `utcnow` for the following Event: '%s'",
                    event,
                )
        
        formatted_event = {