Validate messages sent in `#showcase` and `#resources`.

[pngwn]

Any message sent to #showcase or #resources should contain a link of some sort. If it does then the message is valid.

If the message is not valid then the message should be deleted and user who created the message should receive a DM from the bot stating:

• That all message to the channel they posted to must include a link
• That if they were posting additional information that they should edit their original message or use a thread
• That if they are responding to another users post then they should use a thread.