create a post in a forum channel instead of a thread in a text channel on /pulls commands

do this change on `/pulls` commands using as an example the `octo-forum` channel on discord. This change will do a better visualization on `pull requests channel` and would be more easy to find the pull requests posts.

Start at the `/pulls` command entry point and inspect how it currently creates threads in a text channel. Compare the desired behavior with the `octo-forum` Discord channel example. Done means `/pulls` creates a post in the pull requests forum channel instead of a text-channel thread, making pull requests easier to find.

Written by the indexing model from the issue text.