implement sudo_as_login for Toolkit

[michaelpixelscoder]

Hi,

Following this post on community.shotgunsoftware.com: https://community.shotgunsoftware.com/t/shotgunauthenticator-create-script-user-implement-sudo-as-login/10549

I submit this MR to see if it could be merged on your side.

Motivations:

• When using ShotgunToolkit on the render farm the only way to do operations in the name of the user is to serialize the user session to the render farm. But the session will expire quickly.
• This was only doable using the shotgun_api3 before and doing operations like opening a work scene updating references using breakdown and re publishing was not possible in the name of the user.

This MR contains:

• Implement sudo_as_login argument to ShotgunAuthenticator.create_script_user with unit test
• Change behavior of Configuration._set_authenticated_user to use bootstrap user if sudo_as_login is set.

Hope it can be useful to someone else!

DalteoCraft