Okada Haruki

Add feature to cancel submitted job.

- Fix misspelled word `regist` -> `register`

Rework of https://github.com/line/decaton/pull/80 since it's too outdated. ## Motivation - Currently, DecatonClient serializes tasks in `DecatonTaskRequest` protobuf format because when Decaton had started, Kafka didn't have record header yet *...

- Some applications have a requirement to encrypt message payload end-to-end for security reason - Decaton can provide a feature for that