Add cl_ord_id to spot apis

[claudiapacini]

Is your feature request related to a problem? Please describe.

The Kraken api has introduced the client order id as an alternative to the userref. Unlike the userref the client order id can be a string (e.g database id) and so is very useful.

Describe the solution you'd like

Please add cl_ord_id parameter to all endpoints that accept it, for example https://docs.kraken.com/api/docs/websocket-v2/add_order/

Describe alternatives you've considered

There are no alternatives other than forking this repo and creating a new version that supports cl_ord_id.

[claudiapacini]

i am also happy to do a PR if it will be welcome