Adding files by URL (urlstore)

An experimental IPFS feature allows for files to be added by a provided URL, as far as I can tell `py-ipfs-http-client` does not support this.

I've been using the internal `_client.request` method to make a call to `/urlstore/add` but that is being deprecated with the IPFS daemon giving me the following message: `The 'ipfs urlstore' command is deprecated, please use 'ipfs add --nocopy --cid-version=1 urlstore.go:50`

I tried using `_client.request` to achieve this but was unable to, this API endpoint is a lot more complex, I would like to use features provided by this endpoint.

Please consider implementing support for providing a URL to `/add`.

Thank you.