[guardian] Add Guardian Address Signal Protocol (GASPv1) BIP draft

[bitcoinguardian]

Implements the protocol for the Guardian Address proposal.

The source code for the wallet implementation is available at https://github.com/bitcoinguardian/electrum. This serves as a model for self-custodial wallets, while custodial services may adapt the protocol to their infrastructure.

Guardian Signal tooling is available at https://github.com/bitcoinguardian/GASPv1-draft

A demo with testnet transactions and Guardian integration is available at https://github.com/bitcoinguardian/electrum/tree/master/demo

[bitcoinguardian]

@jonatack I submitted this proposal to the bitcoin-dev mailing list a couple of weeks ago. The email isn't there yet. Do you know if it's still in moderation/review?

[murchandamus]

As described in #1972, this approach overall seems implausible to me, as relying on a compromised device to enforce security is impractical.

[bitcoinguardian]

@murchandamus I've fixed the formatting issues in both BIPs. I believe this proposal is plausible. Please see my response to your concerns in #1972 (comment)