Add better support for GitHub Enterprise Personal Access Tokens PAT

Community ticket: https://community.atlassian.com/t5/Sourcetree-questions/2FA-for-GitHub-Enterprise/qaq-p/2231594?utm_source=atlcomm&utm_medium=email&utm_campaign=&utm_content=post#U2232029

There is no clear way to add an account via personal access token for a GitHub Enterprise account

Steps to reproduce:

1. Tools -> Options -> Authentication -> Add
2. select  "GitHub Enterprise" as the hosting service.
3. Look at list of Authentication options

Currently the selectable Authentication options is "Basic" only.

Desired solution: add: "personal access token" as a second selectable authentication option.

Other git software, such as git fork, has this option.

Workaround solution 1: At the very least there should be an official help article by Atlassian with step by step instructions on how to add an a GitHub personal access token account to Source Tree.  Currently multiple people are posting different ways / workarounds in forums and they either don't work or are hard to follow.