### 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_
else:
            assert b"AccessDenied" in result.content
        # chec
        headers.pop("X-Amz-Decoded-Content-Length")
        result = .put(url, data="test", headers=headers)
        assert result.status_code == 403, (result, result.content)
        if snapshotted:
            exception = xmltodict.parse(result.content)
            snapshot.match("without-decoded-content-length", exception)
        if signature_version == "s3" or not verify_signature:
            assert b"SignatureDoesNotMatch" in result.content
        else:
            assert b"AccessDenied" in result.content
    @markers.aws.validated
    def test_s3_get_response_default_content_type(self, s3_bucket, aws_client):
        # When 
        # 'bin
        # src: 
        # put 
        _key = "key-by-hostname"
        aws_client.s3.put_(Bucket=s3_bucket, Key=_key, Body="something")
        # get 
        url = aws_client.s3.generate_presigned_url(
            "get_", Params={"Bucket": s3_bucket, "Key": _key}
        )
        response = .get(url, verify=False)
        assert response.headers["content-type"] == "binary/octet-stream"
    @markers.aws.validated
    @pytest.mark.parametrize("signature_version", ["s3", "s3v4"])
    def test_s3_presigned_url_expired(