Network Configuration + Legacy Response Comparison Testing

[harrysolovay]

1. There is now a MinaNetwork enum with two variants, Mainnet and Devnet.
2. One now accesses the given network's PG pool by supplying the MinaNetwork.

let pool = mina_mesh.pool(network).await?;

Or in the context of a MinaMesh inherent impl:

let self = self.pool(network).await?;

3. GraphQLClient's send method now accepts the MinaNetwork as an additional argument (note it is in the 0 position).

- self.graphql_client.send(SomeQuery::build(())).await?;
+ self.graphql_client.send(network, SomeQuery::build(())).await?;

5. We now have a utility for asserting equality of the responses of sending the same requests to both MinaMesh and a specified endpoint (for our use, the Ocaml implementation).

let ctx = ResponseComparisonContext::new(mina_mesh, ENDPOINT.to_string());

ctx.assert_responses_eq("/account/balance", req_json).await?;

[piotr-iohk]

Closing in favor of #74.