HIP-35: Update Kraken connector

Rationale

• Due to restrictions on Binance.US and other exchanges, Kraken is currently one of the only crypto exchanges available to US residents
• Its lower fees compared to Coinbase make it more attractive for US-based Hummingbot users
• The current Kraken connector was built originally in early 2020 and has not been updated
• Updating the Kraken connector and allowing it to be used on Hummingbot V2 strategies should increase adoption and usage among US-based users

Description of Work

• Update the spot Kraken connector to the latest spot connector standards
• Add support for spot Kraken candles feed using their OHLCV API - see https://docs.kraken.com/rest/#tag/Market-Data/operation/getOHLCData

Bounty

600,000 HBOT tokens

Developer

To be assigned by Hummingbot Foundation