Implement main passkey backend

Related to #569932

What does this MR do and why?

Implement main passkey backend (controllers, services, helpers & routing)

Screenshots or screen recordings

• BE demo to create and delete passkeys programmatically
• Integrates with the conditional UX & FE logic for default passkeys when at least 1 2FA method is enabled

Demo
passkey_controller_demo

How to set up and validate locally

• Open a rails console

gdk rails console

• Create a user with a WebAuthn registration and verify model changes.

user = User.first
auth1 = user.passkeys.create(
  name: 'LastPass',
  credential_xid: SecureRandom.hex,
  public_key: SecureRandom.hex,
  counter: 0,
  last_used_at: 20.days.from_now,
  authentication_mode: :passwordless
)

auth1.last_used_at
auth1.passkey_eligible

• Go to https://gdk.test:3443/-/profile/two_factor_auth
• Run Feature.enable(:passkeys)
• Play around with the connected UI
• Try to log out & log in with & without 2FA
  • You won't be able to test passkey registration & sign_in yet until other frontend tasks are completed

MR acceptance checklist

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