### Is there an existing issue for this?

- [X] I have searched the existing issues

### Current Behavior

- Localstack fails with HTTP 500, error code "InternalError", message "not enough values to unpack (expected 2, got 1)" when `CopySource` is an invalid string for `copy_object` API.

### Expected Behavior

- For the same API `copy_object`, the cloud fails with HTTP 400, error code "InvalidArgument".
- Localstack should handle invalid `CopySource` i.e., it is a dictionary with one value or an invalid string not adhering to "{bucket}/{key}" format.

### How are you starting LocalStack?

With a `docker run` command

### Steps To Reproduce

#### How are you starting localstack (e.g., `bin/localstack` command, arguments, or `docker-compose.yml`)

    docker run localstack/localstack

#### Client commands (e.g., AWS SDK code snippet, or sequence of "awslocal" commands)

    botoclient.copy_object(CopySource="Invalid_random_string", Bucket="test_bucket", Key=key) 


 test_bucket is a valid bucket.  

### Environment

```markdown
- OS: Ubuntu 22.04.2 LTS
- LocalStack: 2.1.0
- boto3: 1.28.6
```


### Anything else?

_No response_
# GET 
        simple_params = {"Bucket": bucket_name, "Key": _key}
        url = _generate_presigned_url(client, simple_params, expires)
        response = .get(url)
        assert response.status_code == 200
        assert response.content == b"123"
        params = {
            "Bucket": bucket_name,
            "Key": _key,
            "ResponseContentType": "text/plain",
            "ResponseContentDisposition": "attachment;  filename=test.txt",
        }
        presigned = _generate_presigned_url(client, params, expires)
        response = .get(presigned)
        assert response.status_code == 200
        assert response.content == b"123"
        _data = f"this should be found in when you download {_key}."
        # inva
        response = .get(
            _make_url_invalid(s3_url, _key, presigned),
            data=_data,
            headers={"Content-Type": "my-fake-content/type"},
        )
        assert response.status_code == 403
        exception = xmltodict.parse(response.content)
        snapshot.match("invalid-get-1", exception)
        # put 
        response = .put(
            _generate_presigned_url(client, simple_params, expires, client_method="put_"),
            data=_data,