### 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_
snapshot.add_transformer(snapshot.transform.s3_api())
        bucket_name = f"bucket-does-not-exist-{short_uid()}"
        with pytest.raises(ClientError) as e:
            response = aws_client.s3.list_s(Bucket=bucket_name)
        e.match("NoSuchBucket")
        snapshot.match("list_", e.value.response)
        with pytest.raises(ClientError) as e:
            response = s3_vhost_client.list_s(Bucket=bucket_name)
        e.match("NoSuchBucket")
        snapshot.match("list__vhost", e.value.response)
        bucket_vhost_url = _bucket_url_vhost(bucket_name, region="us-east-1")
        assert "us-east-1" not in bucket_vhost_url
        response = .get(bucket_vhost_url)
        assert response.status_code == 404
        bucket_url = _bucket_url(bucket_name, region="us-east-1")
        assert "us-east-1" not in bucket_url
        response = .get(bucket_url)
        assert response.status_code == 404
        bucket_vhost_url = _bucket_url_vhost(bucket_name, region="us-west-2")
        assert "us-west-2" in bucket_vhost_url