add proxy field

[haskell-monad]

// 1. add dependencies
// yarn add hpagent

// 2. usage
import { HttpsProxyAgent } from 'hpagent';
const httpsProxyAgent = new HttpsProxyAgent({
    proxy: 'http://127.0.0.1:7890'
});

const client = new BlockFrostAPI({ projectId: apiKey, proxy: httpsProxyAgent });

[slowbackspace]

Hi, thanks for contribution. Since there are already multiple options that we allow to override one by one, we've decided the better approach would be to add ability to override whatever got option you need by passing single gotOptions object https://github.com/blockfrost/blockfrost-js/pull/293