### 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_
"""
        Test that the response structure is correct for the S3 API
        """
        aws_client.s3.put_(Bucket=s3_bucket, Key="test", Body="test")
        headers = {"x-amz-content-sha256": "UNSIGNED-PAYLOAD"}
        s3_http_client = aws_http_client_factory("s3", signer_factory=SigV4Auth)
        def get_xml_content(http_response_content: bytes) -> bytes:
            # just 
            return http_response_content.replace(b"'", b'"').replace(b"utf", b"UTF")
        # List
        endpoint_url = _endpoint_url()
        resp = s3_http_client.get(endpoint_url, headers=headers)
        assert b'<?xml version="1.0" encoding="UTF-8"?>\n' in get_xml_content(resp.content)