add grpc gateway get endpoint for validator distribution information

[gsk967]

Summary

as per this issue add grpc gateway get endpoint for validator distribution info

Problem Definition

We need to call two endpoints for validator commission rewards and self-delegation rewards. add deprecated endpoint back to distribution module

Proposal

1. Add get service (cosmos/distribution/v1beta1/validators/) in query.proto
2. get service has to return this data

{
 "operator_address": "cosmos1jxv0u20scum4trha72c7ltfgfqef6nscj25050",
    "self_bond_rewards": [
      {
        "denom": "uatom",
        "amount": "188157319.117012814400000000"
      }
    ],
    "val_commission": {
      "commission": [
        {
          "denom": "uatom",
          "amount": "415585935.183993331563784133"
        }
      ]
    }
}