FEATURE: Validate domain settings for blocked_onebox_domain only (#15754)

We want to prevent the user from adding ? or * minimally
when setting domains in sitesettings

lib/validators/host_list_setting_validator.rb

@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+class HostListSettingValidator
+  def initialize(opts = {})
+    @opts = opts
+  end
+
+  def valid_value?(val)
+    val.exclude?("*") && val.exclude?("?")
+  end
+
+  def error_message
+    I18n.t('site_settings.errors.invalid_domain_hostname')
+  end
+end