Go SDK - Add String() method to exported structs for better logging

[wilbred-anto]

Background:
While working with the Looker SDK for Go, I noticed that there is no String() method implemented for the exported structs.
Currently, the absence of a String() method makes it challenging when it comes to logging or debugging, especially considering that many structs contain pointer variables.

Having a String() method would greatly enhance the developer experience by providing a human-readable string representation of the struct. This would be particularly useful for logging and debugging purposes, making it easier to understand the content of structs when working with the SDK.

I understand that the SDK is designed to work with auto-generated code based on Looker API specifications, and I believe that having String() methods for the exported structs could be a valuable addition without compromising the core functionality.