download_file arguments - bucket and key

Currently, the download_file CLI command requires the whole API URL to download the file.

- [ ] Example on how to get the URL.
- [ ] Documentation on how to use the URL in CLI. (passed with " ")

Discussion on how changing from URL to just bucket and key to download the file can be done. The current implementation fetches the API URL from user, parses the bucket and key, and again generates the URL to get a response from the server.