Can add support for koji buildroot overrides?

[praiskup]

In Copr we have this HOWTO wait for the buildroot overrides:

https://github.com/fedora-copr/copr/blob/3c77e83ce735bfc11776615eae00fe910a497c30/doc/how_to_release_copr.rst?plain=1#L153-L161

And I'm proposing this helper snippet for doing overrides: fedora-copr/copr#3166

Both those are manual and complicated tasks for humans, but should be easy for Tito to automatize - we have an appropriately defined list of distributions to release into in .tito/releasers.conf..