Add passkey related controller logic & concern

Related to #569932

• MR 3 of 4
• A series of MRs were segmented from !209582 (closed) to make reviewing easier
  • !211326 (merged) & !211371 (merged) can be merged independently
  • !211467 (previous MRs added as a merge dependency)
  • !211616 (previous MRs added as a merge dependency)
• See !209582 (closed) for more context

What does this MR do and why?

• Adds passkey & session controller logic
• Revises the authenticates_with_2fa concerns to allow for 2fa and passwordless_via_passkey flows
• Adds a combined webauthn_registrations user association for more performant cumulative webauthn queries
• Adds test coverage

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