Add NetworkState Service

[boray]

This PR introduces a new feature to fetch the maximum block height information from an archive node. This information can then be used to check the synchronization of archive nodes with Mina nodes.

The query below returns canonicalMaxBlockHeight and pendingMaxBlockHeight:

query maxBlockHeightInfo {
  networkState {
    maxBlockHeight {
      canonicalMaxBlockHeight
      pendingMaxBlockHeight
    }
  }
}

closes #111

[45930]

Implementation looks good, but I'd like to see more testing, and maybe update the name of the query to allow for expansion in the future.