✨ 💄 Group flags in cobra help output

[wesen]

Closes #59

This adds the unused as of yet parameter CommandGroup for the declarative parameter
yaml struct.

I'm letting this go for now as I still have to hook things up to REST and Lambda and want to
see how much of the declarative part I have to modify anyway.

All other tools don't use the embed yaml pattern either.

• ✨ First pass, ugly output, but proof of concept works
• ✨ Add proper indenting of flags, richer representation of flag usage
• 🎨 Elide output as cobra does
• 🎨 Further customize templated flag usage output
• 🎨 Little tweaks