Documentation update: Gmail SMTP settings

[MuPp3t33r]

Hi folks
Just want to suggest an update to the documentation here:
https://github.com/overhangio/tutor/blob/master/docs/tutorials/google-smtp.rst

specifically related to the "less secure apps" part, this feature is depreciated by Google, users should instead refer to the Application-Specific Passwords feature (https://support.google.com/mail/answer/185833?hl=en) to allow less secure apps to have access to Gmail

Refer below forum post for details:
https://discuss.openedx.org/t/issues-regarding-smtp/12594