### 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_
f"{body}\r\n"
            "0;chunk-signature=78fae1c533e34dbaf2b83ad64ff02e4b64b7bc681ea76b6acf84acf1c48a83cb\r\n"
        )
        url = f"{config.internal_service_url()}/{s3_bucket}/{key_name}?partNumber={1}&uploadId={upload_id}"
        response = .put(url, invalid_data, headers=headers, verify=False)
        assert response.status_code == 500
        # now 
        data = (
            "a;chunk-signature=b5311ac60a88890e740a41e74f3d3b03179fd058b1e24bb3ab224042377c4ec9\r\n"
            f"{body}\r\n"
            "0;chunk-signature=78fae1c533e34dbaf2b83ad64ff02e4b64b7bc681ea76b6acf84acf1c48a83cb\r\n"
        )
        response = .put(url, data, headers=headers, verify=False)
        assert response.ok
        part_etag = response.headers.get("ETag")
        assert not response.content
        # vali
        assert part_etag.strip('"') == precalculated_etag
        multipart_upload_parts = [
            {
                "ETag": part_etag,
                "PartNumber": 1,
            }
        ]
        aws_client.s3.complete_multipart_upload(
            Bucket=s3_bucket,
            Key=key_name,
            MultipartUpload={"Parts": multipart_upload_parts},
            UploadId=upload_id,
        )