Move repo to a PNPM workspace - CLOSED

We've been using [PNPM](https://pnpm.io/) to surface issues with dependencies across the DCR / AR repo. Because of the way PNPM handles dependencies without hoisting (and therefore not combining dependencies across projects) it's more useful in this regard than Yarn.

As such we've now reached a point where we're able to add each of the projects to a PNPM workspace.

Does anyone have any objection to this idea?