fix: downcase email before finding (#8921)

* fix: downcase email when finding

* feat: add `from_email` class

* refactor: use `from_email`

* feat: add rule to disallow find_by email directly

* chore:  remove redundant test

Since the previous imlpmentation didn't do a case-insentive search, a new user would be created, and the error would be raised at the DB layer. With the new changes, this test case is redundant

* refactor: use from_email

app/controllers/devise_overrides/passwords_controller.rb

@@ -5,7 +5,7 @@ class DeviseOverrides::PasswordsController < Devise::PasswordsController
   skip_before_action :authenticate_user!, raise: false
 
   def create
-    @user = User.find_by(email: params[:email])
+    @user = User.from_email(params[:email])
     if @user
       @user.send_reset_password_instructions
       build_response(I18n.t('messages.reset_password_success'), 200)

app/controllers/devise_overrides/sessions_controller.rb

@@ -33,7 +33,7 @@ class DeviseOverrides::SessionsController < DeviseTokenAuth::SessionsController
   def process_sso_auth_token
     return if params[:email].blank?
 
-    user = User.find_by(email: params[:email])
+    user = User.from_email(params[:email])
     @resource = user if user&.valid_sso_auth_token?(params[:sso_auth_token])
   end
 end

app/controllers/platform/api/v1/users_controller.rb

@@ -8,7 +8,7 @@ class Platform::Api::V1::UsersController < PlatformController
   def show; end
 
   def create
-    @resource = (User.find_by(email: user_params[:email]) || User.new(user_params))
+    @resource = (User.from_email(user_params[:email]) || User.new(user_params))
     @resource.skip_confirmation!
     @resource.save!
     @platform_app.platform_app_permissibles.find_or_create_by!(permissible: @resource)