Override the fallback repository for shared config with KODIAK_FALLBACK_CONFIG_REPO

[1oglop1]

I am planning to replace buldozer with kodiak and buldozer has default setting in a single repo without fallback to .github repository.
I'd like to preserve that functionality and allow self-hosted Kodiak to fall back to a different repo other than .github.

Here is a fork with proposed change, please let me know if you are interested in PR master...jans-forks:kodiak:master

[chdsbd]

Hey @1oglop1, thanks for opening this issue.

I think the .github repository is a good solution for shared configuration and I don't see this change as being useful for most Kodiak users.

Only self-hosting users would be able to access this proposed configuration option.

[1oglop1]

I do not know much about .github repo, this is the first time I am reading about it, is that any kind of documented standard I've missed in docs?

[chdsbd]

@1oglop1 I'd have to look more, but I think using a .github repository as a way to centralize GitHub configuration has been around for a while. I found this page on the GitHub docs that mentions it: https://docs.github.com/en/communities/setting-up-your-project-for-healthy-contributions/creating-a-default-community-health-file#about-default-community-health-files

This was the original issue to support it in Kodiak: #403