Update price API

[HDauven]

The current price API used is the Uniswap V2 subgraph. The NII price is calculated based off of the Uniswap V2 Ethereum price in USDT and the NII/ETH pair ratio. Implementation details can be found here.

The code base could be simplified significantly by using the CoinGecko price API directly by retrieving the NII price in USDT.

CoinGecko API documentation can be found here.

A potential approach could be to call the following endpoint:
https://api.coingecko.com/api/v3/coins/nahmii?localization=%22EN%22&tickers=true&market_data=true&community_data=false&developer_data=false&sparkline=false

The resulting structure has the following data that might be relevant:

{
  ...
  "market_data": {
    "current_price": {
      ...
      "usd": 0.00692759,
      ...
    },
}

This USD value can be used to replace most of the code that currently lives in the thegraph-calls.js file.