[FEATURE] Add a command to manipulate the player's blush asset

[SandrinePDR]

This adds the /blush chat command with the following options:

• '+' increase the blushing by one level
• '-' decrease the blushing by one level
• 'min' sets the blushing to the lowest available level
• 'max' maximizes the blushing

This should work, regardless of the chosen blush asset, in case we have more in the future.