Google captcha integration #2524

Initially reported on https://github.com/mautic/mautic/issues/2524

Description:
The CAPTCHA version of mautic form is quite basic. As you may know, Google has developed an open source reCAPTCHA which is quite powerful.
recaptacha
It would be very nice that this feature is integrated instead (or furthermore) of the existing CAPTCHA.
I found a piece of doc there :slight_smile:
https://developers.google.com/recaptcha/old/docs/php

See also existing plugin. I think we should consider adding it in the mautic core. https://github.com/KonstantinCodes/mautic-recaptcha