return token acces GCP via curl commands

[pentium10]

As more and more APIs, especially around Gemini and LLM powered features of various Google Cloud products are not copied quickly over in the library as methods, and if they are copied, they are copied with PHP ~8.4 implementation details.

To overcome this limitation, would be easier if we could return the token via this repo's functions, and use that to call CURL calls against these new APIs.

This request is to document how to return the token, and use in plain CURL calls + sample.