final isolation repo cleanup

[vilmibm]

Closes #1405
Part of #1082

This PR:

• isolates the repo credits easter egg
• removes command/repo.go in favor of pkg/cmd/repo/repo.go

I could have gone farther and re-exported the various NewCmd* functions from the new repo package
but it didn't seem worth it right now.

[mislav]

Looks good!

I wonder if the Command in pkg/cmd/repo/repo.go should nest other repo commands underneath it, or should it remain the responsibility of root.go to properly create a command tree? Right now it does not matter either way, so let's leave it as-is for now and revisit later based on how we feel.

[vilmibm]

I couldn't decide either way and figured we could punt on it as you suggest. I kind of like every AddCommand being in one place but it does make for a very long root.go.