Move SCM details to GitHub branch source plugin

[timja]

Updated GitHub branch source plugin and can see SCM details:

There is a removal of functionality for people not using the GitHub branch source plugin, I think some of what was added to GitHub branch source needs moving to the Git plugin.

Better to merge this though as otherwise people on latest pipeline graph view will have double details, one provided by github branch source and one from here

Testing done

Submitter checklist

• Make sure you are opening from a topic/feature/bugfix branch (right side) and not your main branch!
• Ensure that the pull request title represents the desired changelog entry
• Please describe what you did
• Link to relevant issues in GitHub or Jira
• Link to relevant pull requests, esp. upstream and downstream changes
• Ensure you have provided tests that demonstrate the feature works or the issue is fixed