chore: define patterns for client-side data fetching

[helmturner]

We're stubbing data for these at the moment, so we'll need to wire up fetchers and such. See src/components/ProposalForm.tsx for the current pattern being used for this.

[helmturner]

I'm going to narrow the scope of this and create a new issue for the other requests. I think defining a strategy for client fetching is enough to consider this one closed.