### 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_
for encoding in None, "gzip":
            # put 
            _key = "key-by-hostname"
            aws_client.s3.put_(
                Bucket=s3_bucket,
                Key=_key,
                Body="something",
                ContentType="text/html; charset=utf-8",
            )
            url = aws_client.s3.generate_presigned_url(
                "delete_", Params={"Bucket": s3_bucket, "Key": _key}
            )
            # get 
            headers = {}
            if encoding:
                headers["Accept-Encoding"] = encoding
            response = .delete(url, headers=headers, verify=False)
            assert not response.content
            assert response.status_code == 204
            # AWS 
            assert response.headers.get("content-length") in [
                "0",
                None,
            ], f"Unexpected content-length in headers {response.headers}"
    @markers.aws.validated
    def test_head_has_correct_content_length_header(self, s3_bucket, aws_client):