Move ibc-rs repository to cosmos organization

[ebuchman]

To facilitate discovery of this repo within the Cosmos world, and since it's becoming core to Cosmos dev (especially Hermes), we should move this repo to https://github.com/cosmos/.

In principle this is a simple transfer operation and Github will handle redirects, but to avoid any potential breaks to existing workflows right now, we will target end of June July for this (ie. after DeX launch :) )

[adizere]

Superseded by #2639.