Chain-prometheus-exporter: Expand to monitor number of transactions

[Thahara]

The service currently monitors the account balance for a list of account, we would like for it to also monitor the number of transactions theses accounts have made.

Not sure if this data is easily available from chain, but one option is to fetch it from the CCDScan api via GraphQL query:

query {
  accountByAddress(
    accountAddress: "4MwARWeXdMs3YZ5MPPn2561ceani6AJAVTNPtwS6tceaG2qatK"
  ) {
    transactionCount
  }
}

Which returns:

{
  "data": {
    "accountByAddress": {
      "transactionCount": 68834832
    }
  }
}