Remove Yahoo login support from core and deprecate OpenID2.0 (#7310)

- Plugin developers using OpenID2.0 should migrate to OAuth2 or OIDC. OpenID2.0 APIs will be removed in v2.4.0

- For sites requiring Yahoo login, it can be implemented using the OpenID Connect plugin: https://meta.discourse.org/t/103632

For more information, see https://meta.discourse.org/t/113249

lib/auth/open_id_authenticator.rb

@@ -35,6 +35,7 @@ class Auth::OpenIdAuthenticator < Auth::Authenticator
   end
 
   def after_authenticate(auth_token, existing_account: nil)
+    Discourse.deprecate("OpenID Authentication has been deprecated, please migrate to OAuth2 or OpenID Connect", since: "2.3.0beta4", drop_from: "2.4")
     result = Auth::Result.new
 
     data = auth_token[:info]