Make the bot POTD statement more fun by randomizing the daily message

[volkmchl]

The discord bot that publishes the daily Leetcode problem publishes the link and an additional message per difficulty in https://github.com/code-chronicles-code/leetcode-curriculum/blob/main/workspaces/post-leetcode-potd-to-discord/src/getPotdMessage.ts.

We can make the message more fun by having more random messages for each difficulty level.

[miorel]

Releasing this for now, @volkmchl feel free to reclaim it if you plan to work on it.