Create github repo on course creation

[marslanabdulrauf]

What are the relevant tickets?

https://github.com/mitodl/hq/issues/6962

Description (What does it do?)

This PR:

1. Adds signal COURSE_CREATION to create github repo if the feature ENABLE_AUTO_GITHUB_REPO_CREATION is on
2. If the feature flag is off, remove the giturl when a re-run is created

How can this be tested?

1. Install and configure ol_openedx_git_auto_export
2. Make sure to:
   • Enable ENABLE_AUTO_GITHUB_REPO_CREATION
   • Set GITHUB_ORG
   • Set GITHUB_ACCESS_TOKEN -- This token should have repo read/write and pull/push access.
3. Create a new course
   • Verify if the repo is created in your ORG and have initial commit with empty course
   • Check the giturl setting in advance settings is set properly
   • Check course git repo model in django admin
4. Create Re-Run: No repository will be created for re-runs now
   - If ENABLE_AUTO_GITHUB_REPO_CREATION is enabled -- verify if a new/different repository is created for re-run
   - else: make sure giturl is cleared from course advance settings
5. Make changes to either new course or re-run
   • Verify that the changes are uploaded to respective github respository

Testing management command

1. You must have a course with giturl set in its advance settings -- It shouldn't have gitrepo entry in CourseGitRepo model
2. Run Management command python manage.py cms mirate_giturl [course_id]
3. Verify that the giturl is migrate to CourseGitRepo model
4. Make sure that no url is migrate for re-run courses