WIP documentation of the WebAuthn signature payload

[imalsogreg]

@EnoF what do you think? Is this clear enough?

PR checklist:

• [ ] Test coverage for the proposed changes
• [ ] PR description contains example output from repl interaction or a snippet from unit test output
• [ ] Documentation has been updated if new natives or FV properties have been added. To generate new documentation, issue cabal run tests. If they pass locally, docs are generated.
• [ ] Any changes that could be relevant to users have been recorded in the changelog
• [ ] In case of changes to the Pact trace output (pact -t), make sure pact-lsp is in sync.

Additionally, please justify why you should or should not do the following:

• [ ] Confirm replay/back compat
• [ ] Benchmark regressions
• [ ] (For Kadena engineers) Run integration-tests against a Chainweb built with this version of Pact