Added CORS

[freaker2k7]

I had issues when running the following code in the browser:

import { Address, beginCell, toNano } from '@ton/core';
import { TonClient } from '@ton/ton';

const client = new TonClient({ endpoint: 'http://localhost:8082/jsonRPC' });

const contractAddress = Address.parse('0:1da77f0269bbbb76c862ea424b257df63bd1acb0d4eb681b68c9aadfbf553b93');

const totalBalance = Number(await client.getBalance(contractAddress)) / 1e9;

When await client.getBalance() was throwing a CORS error in the browser.

So I added CORS support to the FastAPI server.