### 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)

connection_name = "This should fail with two errors 123467890123412341234123412341234"
        with pytest.raises(ClientError) as ctx:
            aws_client.events.create_connection(
                Name=connection_name,
                AuthorizationType="INVALID",
                AuthParameters={"BasicAuthParameters": {"Username": "user", "Password": "pass"}},
            ),
        assert ctx.value.response["ResponseMetadata"]["HTTPStatusCode"] == 400
        assert ctx.value.response["Error"]["Code"] == "ValidationException"
        message = ctx.value.response["Error"]["Message"]
        assert "3 validation errors" in message
        assert "must satisfy regular expression pattern" in message
        assert "must have length less than or equal to 64" in message
        assert "must satisfy enum value set: [BASIC, OAUTH_CLIENT_CREDENTIALS, API_KEY]" in message
    @markers.aws.unknown
    def test_put_events_with_target_firehose(self, aws_client, clean_up):