Sync the .packit.yaml config to downstream repo

[psss]

The config file needs to be present in the rawhide branch of dist-git to actually enable the propose_downstream feature. Let's keep the file in sync.

[LecrisUT]

I don't remember if it's the spec file or the packit config that is synced by default, but it's good to have them both explicitly

[psss]

I don't think there is any default value, packit docs state that only packit init would default for the two files:

Spec file path and config file path are always included by packit init but can be manually removed from the list.