feat/QB-2231: Add metrics api for x/pot

[BoThe1K]

from localnetwork ex

{
   "height" : "10449",
   "result" : {
      "chain_mining_reward" : "16000000000000000000",
      "circulation_supply" : "59999500000000000000000000",
      "meta_mining_reward" : "16000000000000000000",
      "resource_mining_reward" : "48000000000000000000",
      "total_bonded_delegation" : "500000000000000000000",
      "total_mined_tokens" : "0",
      "total_mining_reward" : "80000000000000000000",
      "total_mining_supply" : "40000000000000000000000000",
      "total_resource_nodes_deposit" : "0",
      "total_supply" : "100000000000000000000000000",
      "total_unbonded_delegation" : "0",
      "total_unbonding_delegation" : "0"
   }
}