Draft: Add GPG namespace

[sebastinez]

This PR proposes the implementation of the GPG namespace.

Discussion is located in #65

[bumblefudge]

Discussed at last meeting, leaving open pending as-yet undefined Namespaces policy on non-chain crypto systems. At this meeting, we also noted we should document better where new namespace definiions will go (/namespaces/). We also discussed the distinction between caip:gpg and caip:gpg-vks (https://keys.openpgp.org/about/api)-- how VKS could fit was discussed.

[bumblefudge]

Removed next meeting tag and will return to this issue after editorial namespace overhaul and discussions of non-chain boundary of this group's scope

[silverpill]

What's the status of this?
Are non-blockchain namespaces allowed?

[obstropolos]

Doing some cleanup here - we've now moved all namespace requests to the namespaces repo. If this discussion is to continue, please reopen this in the namespaces repo: https://github.com/chainagnostic/namespaces - thanks!