[darc/maestro++] "darc clone" should try to use GitHub URLs automatically when an AzDO repo is specified but no authentication is given

- [ ] This issue is blocking
- [ ] This issue is causing unreasonable pain

We need to be able to use the tagged state of the `Version.Details.xml` in dotnet/installer to clone repos with `darc clone`. For internal servicing builds, the tagged state contains internal repos that `darc clone` needs to handle by cloning from GitHub instead. This is similar to the issue with internal sources ending up in `nuget.config`.

See https://github.com/dotnet/arcade/issues/6027 for more details.

(The source-build team will probably work on this. /cc @crummel @dseefeld )