### 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_
)
        custom_hostname = "foobar"
        monkeypatch.setattr(
            config,
            "LOCALSTACK_HOST",
            config.HostAndPort(host=custom_hostname, port=config.GATEWAY_LISTEN[0].port),
        )
        key = "test.file"
        content = "test content 123"
        acl = "public-read"
        # uplo
        response = s3_multipart_upload(bucket=s3_bucket, key=key, data=content, acl=acl)
        snapshot.match("multipart-upload", response)
        expected_url = (
            f"{_bucket_url(bucket_name=s3_bucket, localstack_host=custom_hostname)}/{key}"
        )
        assert response["Location"] == expected_url
        # down
        downloaded_ = aws_client.s3.get_(Bucket=s3_bucket, Key=key)
        snapshot.match("get-", response)
        assert content == to_str(downloaded_["Body"].read())
        # down
        download_url = response["Location"].replace(
            f"{get_localstack_host().host}:", "localhost.localstack.cloud:"
        )
        response = .get(download_url)
        assert response.status_code == 200
        assert to_str(response.content) == content
    @markers.aws.only_localstack
    def test_s3_hostname_with_subdomain(self, aws_http_client_factory, aws_client):