https://www.okx.com/docs-v5/en/
https://www.okx.com/docs-v5/en/#public-data-rest-api-get-funding-rate
https://www.okx.com/docs-v5/en/#public-data-rest-api-get-funding-rate-history
https://www.okx.com/docs-v5/en/#public-data-rest-api-get-mark-price
https://www.okx.com/docs-v5/en/#public-data-rest-api-get-underlying