Migrate WebAuthn authentication workflow from jQuery to Vue

Similar to the work we have done with the WebAuthn registration, Frontend: Enable WebAuthn device registration w... (!111659 - merged), I propose to migrate the WebAuthn authentication (https://gitlab.com/gitlab-org/gitlab/-/blob/master/app/assets/javascripts/authentication/webauthn/authenticate.js) to Vue.

This type of migration has many advantages:

• more maintainable and commonly understood
• reuse of Vue components (buttons, forms, alerts) that get updated and improve continously
• opportunity to improve the look and feel
• remove the jQuery dependency (large dependency)

Part of this:

• remove old fixtures
• update feature and e2e tests
• remove unneeded helpers

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Implementation Plan Draft:

Part 1 - Introduce Feature flag:

• In authentication/webauthn/index.js add initWebauthnAuthenticateVue. Can be NO-OP initially.

• In authentication/webauthn/index.js add initWebauthnAuthenticateLegacy.

• Refactor initWebauthnAuthenticate to call either version depending on feature flag presence.

• In each devise auth controller action (there are 4), inject feature flag to expose to frontend.

• Create No-OP haml template called _totp_recovery_code_or_webauthn_vue.html.haml

• In devise/shared/_totp_recovery_code_or_webauthn.html.haml#L19 use feature flag to conditionally render either _totp_recovery_code_or_webauthn.html.haml or _totp_recovery_code_or_webauthn_vue.html.haml

Part 2 - Implement Vue component:

• _totp_recovery_code_or_webauthn_vue.html.haml will be a stripped file that only contain's the dom node too bootstrap the Vue app, and pass in params via the HTML5 data-attribute.
• Create webauthn_authenticate.vue component to contain the text markup from the haml template AND the javascript logic from authentication/webauthn/authenticate.js

Part 3 - Update tests + testing

• Update unit tests, feature and E2E tests
• Manual regression testing.