I need a way to configure webhook notifications similar to slack but on gchat, i am able to trigger gchat msg via webhook on gchat but cant do the same via checkmk config & notification.
As Elias noted in the first comment on that tread, Checkmk does not support this out of the box so you will need to build something custom.
I haven’t looked at the existing script, but Robert’s comment (that you linked), suggests that it should be fairly easy to adapt it to suit your needs.