Add support for decentralized Exchanges

[scientes]

a list of all: https://coinmarketcap.com/rankings/exchanges/dex/

i would start by implementing at least one for ethereum(uniswap) and one for bsc(pancakeswap) via the apis

https://bscscan.com/ https://etherscan.io/

I think if we implement it for one exchange per chain, we would have a pretty good starting point, also because this could be a larger project I would split it up into multiple issues

[provinzio]

is ccxt capable of querying prices for these exchanges?