graphql-client: debug option

Problem/Motivation

The graphql-client class should accept a debug option which will enable debug logging using the provided logger.

Proposed resolution

Implementation should be similar to other packages, we mainly need to honor the option and add logging where necessary.

Remaining tasks

* Implement changes.
* Add test coverage.
* Update docs.

API changes

graphql-client class will accept a 'debug' option.