How to add custom GitHub Apps in Azure DevOps?

Hello!

We have quite a large mono repo and more than 30-40 teams participate and we have more than 150+ pipelines that get triggered for team-specific commits. We use the default Azure pipelines GitHub App to connect the Azure DevOps with GitHub repos. Since it's a large request considerably other repos also utilize this app in our organization. 

We started getting the GitHub rate limit issue as the Azure Pipelines GitHub app gets about 15000 requests per hour at least twice or thrice a day. So, the GitHub support suggested creating a custom GitHub app and using some of the Azure pipelines to use the new app. 

We need some help on how to add the custom-created GitHub app in Azure DevOps. We can only see OAuth App integration for GitHub, but how to add GitHub Apps integration? If we use the OAuth App integration we get repos not available when the new custom app actually has access to the repos.

Thanks,

Sundar.