### 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_
"Content-Md5": content_md5,
            "Content-Type": "application/octet-stream",
            "User-Agent": (
                "aws-sdk-java/1.11.951 Mac_OS_X/10.15.7 OpenJDK_64-Bit_Server_VM/11.0.11+9-LTS "
                "java/11.0.11 scala/2.13.6 kotlin/1.5.31 vendor/Amazon.com_Inc."
            ),
            "X-Amz-Content-Sha256": "STREAMING-AWS4-HMAC-SHA256-PAYLOAD",
            "X-Amz-Date": "20211122T191045Z",
            "X-Amz-Decoded-Content-Length": str(len(_data)),
            "Content-Length": str(len(_data_chunked)),
            "Connection": "Keep-Alive",
            "Expect": "100-continue",
        }
        url = aws_client.s3.generate_presigned_url(
            "put_",
            Params={
                "Bucket": s3_bucket,
                "Key": _key,
                "ContentType": "application/octet-stream",
                "ContentMD5": content_md5,
            },
        )
        result = .put(url, data=_data_chunked, headers=headers)
        assert result.status_code == 200, (result, result.content)
    @markers.aws.validated
    @markers.snapshot.skip_snapshot_verify(
        condition=is_v2_provider,
        paths=["$..ServerSideEncryption"],
    )
    def test_delete__tagging(self, s3_bucket, snapshot, aws_client):