Integrate with conformance cucumber tests

[lance]

The cloudevents/conformance repository now has HTTP transport cucumber specifications. This SDK should integrate these into the tests.

Ref: https://github.com/cucumber/cucumber-js

[helio-frota]

Going to assign that to me and start playing with. In case things get delayed (until next week) I remove the assignment 👍

[helio-frota]

removing the assignment. I can revisit if needed later, also short week for me here.