Passkeys support: Rename Devise::Strategies::Authenticatable => PasswordAuthenticatable

[tcannonfodder]

Rename Devise::Strategies::Authenticatable => PasswordAuthenticatable

• To begin the process of refactoring Devise to support passkeys (https://github.com/heartcombo/devise/issues/5527), we need to decouple authentication from being specifically tied to passwords.
  • The first step is explicitly prefixing generically-named components like Authenticatable with Password, since they concern password authentication

Add Devise::Strategies::Authenticatable shim w/ deprecation warning

• To maintain compatability with exisiting installations, we need the Devise::Strategies::Authenticatable class.
  • This re-adds the class in, subclassing from PasswordAuthenticable and printing a deprecation warning