Added background script support

Google recommend the script can be placed in the background of the pages for analytics.

The current approach only supports that script can only be applied to form.

If the user wants to have the script to be running on every page of the site, the current approach does not satisfy the requirement.

This release resolved the above issue.

e.g.

{!!  GoogleReCaptchaV3::background() !!} in bottom of your page.