feat(APIError): New Python error class giving access to API response

[ob1-dev]

This change introduces a new APIError class (inheriting from SDKError) which takes one argument of the api_response which should be the JSON payload from the Looker endpoint.

This gets loaded by the class and made accessible as the APIError.api_response property.

The idea is to give simpler access to the type of error that was received from the endpoint in order to take different actions.

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Fixes #723 🦕

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[ob1-dev]

@googlebot I signed it!

[jkaster]

Thanks for your submission. We've implemented the functionality in a similar PR. #1170

[jkaster]

There wasn't anything wrong with your PR, but this was something we already had in process. Thanks again for your contribution. You definitely saw the need!