### 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_
client, simple_params, expires, client_method="delete_"
        )
        response = .delete(presigned_delete_url)
        assert response.status_code == 204
    @pytest.mark.parametrize(
        "signature_version, use_virtual_address",
        [
            ("s3", False),
            ("s3", True),
            ("s3v4", False),
            ("s3v4", True),
        ],
    )
    @markers.aws.validated
    def test_presigned_url_signature_authentication_multi_part(
        self,
        s3_create_bucket,
        signature_version,
        use_virtual_address,
        patch_s3_skip_signature_validation_false,
        aws_client,
    ):
        # it s
        bucket_name = f"presign-{short_uid()}"
        s3_endpoint_path_s = _endpoint_url()
        s3_create_bucket(Bucket=bucket_name)
        _key = "temp.txt"
        s3_config = {"addressing_s": "virtual"} if use_virtual_address else {}
        client = _s3_client_pre_signed_client(
            Config(signature_version=signature_version, s3=s3_config),