Assign creatorAddress in handleSubgraphPublishedV2

[mnlesane]

The creatorAddress field has not been assigned for subgraphs created after 2022-02-23, as the graphAccount param is no longer associated with the SubgraphPublished event for v2. This PR uses event.transaction.from instead.

Demonstration:
https://thegraph.com/hosted-service/subgraph/mnlesane/graph-network-mainnet

  subgraphs(orderBy:createdAt, orderDirection:desc
  ) {
    id displayName creatorAddress
  }
}```

[juanmardefago]

Hey @mnlesane!
Looks good! I'm going to merge it to mainnet-staging now that we got the workflows back to a state where it's only going to be deploying to staing on pushes there.

I'm also gonna merge #182 there, and check if everything works as expected afterwards, before moving it to production!

Thanks a ton for the contributions and sorry for the long delays!