Description of problem:

When attempting to create a PR in a GitHub Enterprise repo via the “Register Existing Component” flow, it fails with an error stating that no auth provider is available for the enterprise host, despite the host being correctly configured in `integrations.github`.

Fix: We would have to read the configs here, and instead of calling ScmAuth.createDefaultApiFactory(), we would need to create a custom API factory for SCM auth like this (and pass in the host config)

Steps to Reproduce

1. Configure GitHub Enterprise integration in app-config
2. Register existing component
3. Try to register a GitHub repo that does not have an existing catalog-info.yaml
4. The catalog import plugin will try to create a catalog-info.yaml and create a PR in the repo, but error will occur here because the SCM auth provider for the enterprise host does not exist

Actual results:

`No auth provider available for https://github-\

', see https://backstage.io/link?scm-auth`
 

Expected results:

The enterprise host configs should be used to create the required SCM auth provider

Reproducibility (Always/Intermittent/Only Once):

Always

Build Details:

Additional info (Such as Logs, Screenshots, etc):