#5131 Feat/Add CoinFLEX Connector

This PR adds a connector for the CoinFLEX.com exchange: https://www.coinflex.com/

We'd love to have a successful & long-term relationship with the Hummingbot community. Love the ethos of the foundation and what it stands for.

Highlights of CoinFLEX: (1) 1st to have a crypto Repo market, where borrowers & lenders can interact directly on orderbook. Repo is a spread between Spot & Perps.
(2) flexUSD: pegged 1:1 to USDC, minted/redeemed instantly (without lock-up), the 1st ever interest-earning stablecoin, which pays interest every 8 hrs (just by having flexUSD). "Tokenized basis" (no directional risk, delta-neutral), lending dollars directly into Repo markets, Repo is fully collateralized. The last 6 mos / 12 mos APY: 12%.
(3) 1st to have a CeFi AMM+ model: which has access to 10x leverage (capital efficiency). Single currency / cross collateral - can AMM+ two-sided (i.e. someone can use Doge to AMM in ETH/USD perps). With faster matching engines, no gas fees, and lower taker fees (plus leverage on both sides of the trade), our AMM+ model trades more than the average DEX. By default all AMM+ users are on the highest VIP-6 (-3 bps Maker Rebates). Scalping profits in USD by the AMM+ bots. (4) 1st to introduce physically delivered futures for crypto, which has evolved to having the only existing "physically deliverable perpetual swaps" (can convert perp position to spot).

And more innovations to come!

https://github.com/hummingbot/hummingbot/pull/5131