### 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_
self, s3_bucket, aws_client, aws_http_client_factory
    ):
        """
        Different languages don't always handle the space character the same way when encoding URL. Python uses %20
        when Go for example encodes it with `+`, which is the form way. This leads to a specific edge case for
        the CopySource header.
        """
        _key = "test key.txt"
        dest_key = "dest-key"
        aws_client.s3.put_(Bucket=s3_bucket, Key=_key, Body="test-body")
        s3_http_client = aws_http_client_factory("s3", signer_factory=SigV4Auth)
        bucket_url = _bucket_url(s3_bucket)
        copy__url = f"{bucket_url}/{dest_key}"
        copy_source = f"{s3_bucket}%2F{_key.replace(' ', '+')}"
        copy_resp = s3_http_client.put(
            copy__url,
            headers={
                "x-amz-content-sha256": "UNSIGNED-PAYLOAD",
                "x-amz-copy-source": copy_source,
            },
        )
        assert copy_resp.ok
        head_ = aws_client.s3.head_(Bucket=s3_bucket, Key=dest_key)
        assert head_["ResponseMetadata"]["HTTPStatusCode"] == 200
    @markers.aws.validated
    @pytest.mark.parametrize(
        "use_virtual_address",
        [True, False],
    )
    def test_url_encoded_key(self, s3_bucket, aws_client_factory, snapshot, use_virtual_address):