🍱 Generate categorised / formatted `!commands` card automatically

[izzylys]

Currently, the !commands card is populated manually in order to categorise the commands and format the card nicely. This works well enough for now, but it would be useful to eventually have this card be generated automatically to prevent extra work / mistakes in forgetting to update this as new commands are added / removed.

This will likely require some form of custom attributes on our commands to tag them with the correct categories.