Design workspaces support

We need to design what workspaces will look like in `ds`. We should discuss what needs need to be fulfilled and examine the space a bit to see what others have done and how it can be improved on.

Some things I'd really like to have:

* Easy running of commands in sub-packages.
* Nested workspaces.
* Central version management for shared packages.
* Easy cross-subpackage dependency definitions (don't just rely on paths, maybe? -- I think pnpm does an interesting bit here, but maybe Yarn's approach of plain version definitions is better?).
* Look at https://bit.dev/ for more inspiration on monorepo management.
* As a stretch goal, we should have Lerna-like features for publishing subpackages.