### 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, monkeypatch, patch_s3_skip_signature_validation_false, aws_client
    ):
        aws_client.s3.put_(Body="test-value", Bucket=s3_bucket, Key="test")
        presigned_request = aws_client.s3.generate_presigned_url(
            ClientMethod="get_",
            Params={"Bucket": s3_bucket, "Key": "test"},
            ExpiresIn=2,
        )
        # slee
        time.sleep(3)
        # atte
        response = .get(presigned_request)
        # resp
        # "Sig
        assert response.status_code in [400, 403]
        # set 
        monkeypatch.setattr(config, "S3_SKIP_SIGNATURE_VALIDATION", True)
        response = .get(presigned_request)
        assert response.status_code == 200
        assert b"test-value" == response.content
    @markers.aws.validated
    def test_delete_has_empty_content_length_header(self, s3_bucket, aws_client):