EN-7874: Rest API endpoint for economics data

[bogdan-rosianu]

Added a new endpoint /node/economics that will return the economics data for the last epoch. It is available for both meta nodes and shard nodes.

Note that the values are returned in string format and the denomination is included.

Example output:

{
  "data": {
    "metrics": {
      "erd_dev_rewards": "0",
      "erd_epoch_number": 2,
      "erd_inflation": "14030640106544902492",
      "erd_total_fees": "350000000000000",
      "erd_total_supply": "20000027511395306950789200"
    }
  },
  "error": "",
  "code": "successful"
}

Testing procedure:

1. run a testnet with this branch and make sure that api.toml has this endpoint enabled
2. open /node/economics endpoint (of type GET) on multiple nodes.
   2.1. in epoch 0, only the total supply value should be populated
   2.2. after passing in a new epoch, the values will update and should be the same for all the nodes.

[LucianMincu]

System tests passed.