Repo Onboarding: offer Github App to facilitate repo onboarding

### Component

Other

### Describe the feature

The repo blueprint onboarding step is a little clunky. The more Github native way to support such an interface is through a [Github Application](https://docs.github.com/en/apps). It would also allow keeping the IaC source code static while supporting multiple repos in an org.

The IaC deployment would have to be updated to deploy an endpoint to receive the [webhook repo events](https://docs.github.com/en/apps/creating-github-apps/writing-code-for-a-github-app/building-a-github-app-that-responds-to-webhook-events).

### Use case

Having to update the CDK blueprint for each repo and providing a PAT for auth is not the best way to support interfacing with Github repos.

### Proposed solution

_No response_

### Other information

_No response_

### Acknowledgements

- [x] I may be able to implement this feature
- [x] This might be a breaking change