Resolve "BE or FE - Implement add passkey controller/route/view placeholder"

What does this MR do and why?

• Adds Passkeys creation controller/route/haml scaffolding behnd a feature flag.

• adds new "~/profile/passkeys/new" route/template rendered

• adds stubbed out create endpoint without haml template for now since the endpoint will be hit from the two_factor_auths page template

• adds stubbed out destroy endpoint without haml template for now since the endpoint will be hit from the two_factor_auths page template

References

Screenshots or screen recordings

Flag off	Flag on

How to set up and validate locally

• Navigate to https://gdk.test:3000/-/profile/passkeys/new
• Observe 404
• Enable :passkeys feature flag in rails console
• Refresh page
• Observe Empty page

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #569948 (closed)