Support a HTMX attribute to trigger webauthn

Webauthn is extremely javascript dependent, and requests to the [working group](https://github.com/w3c/webauthn/issues/1255) have seemingly stalled.

Because of the javascript forward nature of webauthn, this also makes it non-obvious how to integrate to htmx. It would be good to have either examples of using webauthn with htmx, or native htmx wrappers to facilitate this. Thanks!