Add OAuth support for login in VsCodium

[pmahend1]

Since the extension is available for VSCodium as well, please support Github authentication/authorization to use the extension effectively. Unless this is done ,the extension doesnt work on VSCodium.

You may add VSCodium as registered OAuth app.

Copy of #1778

[alexr00]

This extension just uses VS Code's built in GitHub Authentication extension. This support would need to be added upstream in the VS Code repo.