FIX: store information about the login method in the database. (#28054)

Previously in these 2 PRs, we introduced a new site setting `SiteSetting.enforce_second_factor_on_external_auth`.

https://github.com/discourse/discourse/pull/27547
https://github.com/discourse/discourse/pull/27674

When disabled, it should enforce 2FA for local login with username and password and skip the requirement when authenticating with oauth2.

We stored information about the login method in a secure session but it is not reliable. Therefore, information about the login method is moved to the database.

lib/auth/default_current_user_provider.rb

@@ -140,6 +140,7 @@ class Auth::DefaultCurrentUserProvider
           end
 
         current_user = @user_token.try(:user)
+        current_user.authenticated_with_oauth = @user_token.authenticated_with_oauth if current_user
       end
 
       if !current_user
@@ -267,6 +268,7 @@ class Auth::DefaultCurrentUserProvider
         client_ip: @request.ip,
         staff: user.staff?,
         impersonate: opts[:impersonate],
+        authenticated_with_oauth: opts[:authenticated_with_oauth],
       )
 
     set_auth_cookie!(@user_token.unhashed_auth_token, user, cookie_jar)