Configure Balancer V2 subgraph for Goerli

[nlordell]

This PR configures our Subgraph initialization to know about the Görli subgraph.

This is the last piece required for Balancer V2 to work on Görli.

Test Plan

Make sure we can query Balancer V2 liquidity on Görli:

% cargo run -p solver -- \
  --baseline-sources BalancerV2 \
  --solver-account 0xA70B6e99FCF41bF78d626a95B8C095b87D4A4285 \ 
  --transaction-strategy DryRun \
  --orderbook-url https://barn.api.cow.fi/goerli/                            
...
2022-07-27T13:53:32.736Z  INFO shared::gas_price_estimation: estimator Web3, networkid 5
2022-07-27T13:53:32.856Z  INFO solver: using baseline sources baseline_sources=[BalancerV2]
2022-07-27T13:53:34.019Z DEBUG shared::sources::balancer_v2::pool_init: initialized registered pools block=7299817 pools=100
...
2022-07-27T13:53:37.348Z DEBUG solver::driver: single run finished ok
...