Add support for filtering comment/event subscriptions based upon the role types

[Kshitij-Katiyar]

          This PR aims to provide filter support upon `Groups` for comment visibility. 

We can use the Application Role in the future to provide filter support on that too, but we think it should be done in a new PR because it would be quite a task. I will let @wiggin77 decide on this.

I am not sure what code be done with the type of group in this PR. Can you please elaborate? @esarafianou

Originally posted by @Kshitij-Katiyar in #894 (comment)