fix: fall back to HTTP/1.1 when global http2 option is enabled

[Deeven-Seru]

Summary

This change mitigates hanging requests reported in #3418 when google.options({http2: true}) is used.

Root cause

The hang occurs in the HTTP/2 request path (googleapis-common) where some GET requests can remain open indefinitely. Since this repo surfaces that path through global options, affected calls appear to hang forever.

What changed

• Added normalization of global options in GoogleApis.options().
• If http2: true is provided globally, emit a warning and force http2: false (HTTP/1.1 fallback).
• Preserved all other global options unchanged.
• Added tests to verify fallback behavior and warning emission.

Tests

• npx mocha build/test/test.options.js --grep "disable http2|not emit warning"
• npx mocha build/test/test.options.js

Notes

This is a defensive mitigation in google-api-nodejs-client until a full HTTP/2 transport fix is available downstream.

[quirogas]

HI @DEVELOPER-DEEVEN , thank you for taking a swing at this bug. unfortunately, the code you are modifying is autogenerated, so the change has to happen upstream. Additionally, falling back to http/1.1 comes with it's own set of security concerns, so we would probably want to implement a more secure fall back.

[Deeven-Seru]

Thanks for the clarification @quirogas . I missed that these files were autogenerated—makes total sense why this can't be merged here.
Regarding the HTTP/1.1 fallback, I understand the security/stability implications of a global downgrade. I'll look into googleapis-common or the upstream generator to see if there's a safer way to handle the hanging request timeouts without forcing a protocol downgrade.
Thanks for the review!