Update slack integration option for Portal comments by portal users

What is the challenge?

Currently, in the slack integration, when selecting an idea, it's not clear that selecting "Portal comment added by category" is the option required when you'd like notifications for when a portal user adds a public comment to an idea

What is the impact?

Confusion when configuring slack integration

Describe your idea

Update "Portal comment added by category" to ""Portal comment added by portal user"