Support URLFile in the upload_file function (#1985)
We would like `predict` functions to be able to return a remote URL rather than a local file on disk and have it behave like a file object. And when it is passed to the file uploader it will stream the file from the remote to the destination provided.
```py
class Predictor(BasePredictor):
def predict(self, **kwargs) -> File:
return URLFile("https://replicate.delivery/czjl/9MBNrffKcxoqY0iprW66NF8MZaNeH322a27yE0sjFGtKMXLnA/hello.webp")
```
This PR adds an additional check to the `upload_file()` handler to call `fh.seekable()` before attempting to seek. This allows instances of `io.IOBase` that do not support seek (like `URLFile`) to be uploaded.
We also add a `name` attribute to `URLFile`. This is used by the `upload_file` function to infer the file extension and mime type.
