[BUG] default GitHub branch name is hardcoded to "master"

[DaveTryon]

Bug Template

Describe the bug
When using the GitHub integration from MakeCode, the new repo defaults to the master branch. GitHub changed their default branch name for new repos to main recently, so I'd expect either the default to be main or to have a way to specify what branch gets used

To Reproduce
Steps to reproduce the behavior:

1. Go to https://makecode.microbit.org/#editor
2. Create a project
3. Click on the GitHub integration icon and save it to a GitHub repo
4. Open the project on https://www.github.com
5. Notice that the default branch is master

Expected behavior
I'd expect the GItHub default of main to be used

Desktop (please complete the following information):

• OS: macOS 11.6
• Browser: Chrome
• Version: 94.0.4606.81

Additional context
Add any other context about the problem here.

[besacode]

Looks like a duplicate of #3452

[abchatra]

@eanders-ms did we implement this?