Automated update for rejected Showcase submissions

[bernard0omnisend]

Pasting this from a thread in the WC Asia '24 Contributor Day issue from @marijago:

Hey! Having contributed to the "Moderate and help write Showcase entries" initiative during WCAsia 2024, I noticed a potential for improvement.

At the moment we're not communicating to the applicants whose submissions we reject. I believe it would be appropriate to send them a follow-up message explaining the reason for rejection and not leaving them hanging. Some automation could be established between choosing rejection reason in the Google Sheet and sending a message. Wdyt?

Since some entries are from several years back, I would recommend rolling out the follow-up communication only to the fresh submissions (starting from Jan 2024).