add attachment url option flag

[jonathanfeng-scale]

Pull Request Summary

includes flag to return presigned s3 url's for attachments
as found here: https://docs.scale.com/reference/list-multiple-tasks

Description

includes flag to return presigned s3 url's for attachments
as found here: https://docs.scale.com/reference/list-multiple-tasks

How did you test your code?

test_get_tasks_returns_attachment

Which of the following have you done to test your changes? Please describe the tests that you ran to verify your changes.

• Created new unit tests in tests/ for the newly implemented methods
• Updated existing unit tests in tests/ to cover changes made to existing methods

Checklist

Please make sure all items in this checklist have been fulfilled before sending your PR out for review!

• I have commented my code in details, particularly in hard-to-understand areas
• I have updated Readme.rst document with examples for newly implemented public methods
• I have reviewed Deployment and Publishing Guide for Python SDK document
• I incremented the SDK version in _version.py (unless this PR only updates the documentation).
• In order to release a new version, a "Release Summary" needs to be prepared and published after the merge