Agent: Add env variable for operator address

Indexer agent currently only derives the first wallet of the mnemonic.
A loop until a derived wallet is found would be pretty nice.

# start.ts
    const network = await Network.create(
      logger,
      ethereum,
      argv.mnemonic,
      argv.indexerAddress,
      argv.publicIndexerUrl,
      argv.graphNodeQueryEndpoint,
      argv.indexerGeoCoordinates,
      argv.operatorAddress,                               // <=
      networkSubgraph,
    )

# network.ts

  static async create(
    parentLogger: Logger,
    ethereum: providers.JsonRpcProvider,
    mnemonic: string,
    indexerAddress: Address,
    indexerUrl: string,
    indexerQueryEndpoint: string,
    geoCoordinates: [string, string],
    operatorAddress: Address,                                                                // <=
    networkSubgraph: Client | SubgraphDeploymentID,
  ): Promise<Network> {
    const subgraph =
      networkSubgraph instanceof Client
        ? networkSubgraph
        : createClient({
            url: new URL(
              `/subgraphs/id/${networkSubgraph.ipfsHash}`,
              indexerQueryEndpoint,
            ).toString(),
            fetch,
            requestPolicy: 'network-only',
          })

    const network = await ethereum.getNetwork()

    let logger = parentLogger.child({
      component: 'Network',
      indexer: indexerAddress.toString(),
    })

    logger.info(`Create wallet`, {
      network: network.name,
      chainId: network.chainId,
    })



     ##############################################################################################
    // Just an idea how to do
    Wallet wallet;
    if(operatorAddress){
      string path = "m/44'/60'/0'/0/"              //hdnode_1.defaultPath; "m/44'/60'/0'/0/0" ... "m/44'/60'/0'/0/1" ... "m/44'/60'/0'/0/2" 
      for(let i=0 ; i< 9 ; i++){
        wallet = Wallet.fromMnemonic(mnemonic,(path + i.toString()); 
        if(operatorAddress == wallet.getAddress()){
          break;
        }
      }

    }
    else{
      // Always m/44'/60'/0'/0/0
      wallet = Wallet.fromMnemonic(mnemonic)
    }
   // Continue as usual 
   ###############################################################################################
    ...

Start at start.ts where Network.create receives the indexer settings, then inspect Network.create in network.ts and its current mnemonic wallet setup. Clarify how operatorAddress should select a derived wallet and preserve the existing default when it is absent. Done means the configured operator address can identify the wallet used by the agent.