Migrate _did DNS from TXT to URI

[expede]

NB: Feature requests will only be considered if they solve a pain

Summary

Problem

The current (draft) spec "The Decentralized Identifier (DID) in the DNS" uses URI records, not TXT. Text records were considered, but they've since chosen URI, likely to to did: being a URI scheme:

3. Use of the 'URI' RRType

DIDs use an URI scheme ('did:'), so the most suitable option to publish DIDs in the DNS is the use of the 'URI' RRType.

Impact

It makes interop more difficult, and our system non-standards based.

Solution

Migrate existing TXT records to URI.

Except there's a problem: it doesn't appear that Route53 supports URI records! This is probably why we have TXT records presently. (Filing this mainly for posterity and tracking)