Integrate Epoch Block Oracle

[hopeyen]

In preparation for the Epoch Block Oracle (EBO) to be the source of true latest valid epochs and latest valid epoch start blocks in the multi-chain world, This PR integrates the EBO subgraph such that indexer-agent,common,service can resolve POIs for subgraph deployments on different networks.

Usage

• Supply indexer-agent startup param endpoint --block-oracle-endpoint
• Make sure your graph node has correct ethereum connections (mainnet, goerli, gnosis, etc)

Updates/Notes

• Hardcoded constant variable of supported network aliasing NetworkAliases for Ethereum mainnet, goerli, and gnosis chain. (Remove once aliasing happens on the EBO subgraph or the graph node.
• When resolving POI for an allocation, query the EBO subgraph for start block number, and then query graph node for the corresponding block hash.
  -- This replaces the previous process: query the network epochManager contract for the current epoch start block, then query the indexer agent's eth client for the block hash.
• We can replace currentEpochs and other getBlock(...).hash calls later on

[tilacog]

LGTM, considering the Epoch Subgraph scope.
I would say that removing rinkeby as an indexed chaing is the only required change on that matter.

[fordN]

Getting close!

[fordN]

LGTM 👍

completed:)