Improve subgraph local deployment testing

[ryley-o]

This repository's testing is great, but additional testing associated with running a subgraph locally can catch many other important bugs. For example, the contents of subgraph.yaml can only be tested in this manner, since testing in matchstick requires us to route events to their appropriate handlers directly.

We already have scripts to test locally (e.g. yarn deploy:local can be used to deploy to local graph node), but defining and documenting some general scripted commands on a contract suite would make sense. See the discussion in this PR in our smart-contracts repo: ArtBlocks/artblocks-contracts#302 (comment)

Ideally, we could incorporate something like what is described in the link above to streamline and document local deployments of subgraphs.