IPLD gateway support

Hey folks, I wanted to get a conversation started about whether Iroh would be interested in supporting the [ipld gateway spec](https://github.com/ipfs/specs/pull/293) I've been working on and to talk about some of the tradeoffs of doing so. 😁 

(probably would like to focus the discussion on readable gateways to start, but writable might be a useful convo down the line too).