Add ability to mention the person requested to do the review

[firasm]

Thanks for this great GH action!

It would be very useful for my workflow to also have the ability to tag/mention the person from whom a review is requested.

Expected Behavior

An additional placeholder, called {{reviewer}} so I could add a comment like:

👋 @{{ reviewer }}, here is a checklist of things you should check

[github-actions[bot]]

👋 @firasm Thank you for raising an issue. We will investigate into the matter and get back to you as soon as possible. Please make sure you have given us as much context as possible.

[bubkoo]

@firasm
The payload of the issue/pr now can be used in placeholders. So we can render reviewers with @{{ payload.requested_reviewers[0].login }}.