[New backend] Azure DevOps OAuth2

Azure DevOps Services/Azure DevOps Server allows creating [OAuth2 applications](https://learn.microsoft.com/en-us/azure/devops/integrate/get-started/authentication/oauth?view=azure-devops) which provides token for interacting with [Azure DevOps Services REST API](https://learn.microsoft.com/en-us/rest/api/azure/devops/).

This is different from Azure AD and requires a separate backend.