Also copy git config include files

[Clockwork-Muse]

Git supports the concept of include files (including conditional includes). This can be handy to, among other things, have different identities based on the cloned repository url, for instance when working in multiple personas.

Unfortunately, currently only the "main" git config is copied over, which means that any such config is broken when using devcontainers.

It would be great if this sort of config could be copied over to make these configs work again

[chrmarti]

Continuing in #3331.