### 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)

for element in pattern_value:
        if (isinstance(element, (str, int))) and (event_value == element or element in event_value):
            return True
        elif isinstance(element, dict):
            element_key = list(element.keys())[0]
            element_value = element.get(element_key)
            if element_key.lower() == "prefix":
                if isinstance(event_value, str) and event_value.startswith(element_value):
                    return True
            elif element_key.lower() == "exists":
                if element_value and event_value:
                    return True
                elif not element_value and not event_value:
                    return True
            elif element_key.lower() == "cidr":
                ips = [str(ip) for ip in ipaddress.IPv4Network(element_value)]
                if event_value in ips:
                    return True
            elif element_key.lower() == "numeric":
                if check_valid_numeric_content_base_rule(element_value):
                    for index in range(len(element_value)):
                        if isinstance(element_value[index], int):
                            continue
                        if (
                            element_value[index] == ">"
                            and isinstance(element_value[index + 1], int)
                            and event_value <= element_value[index + 1]