Log server error responses without -GoogleGenerativeAIDebugLogEnabled

[andrewheard]

Updated logging to print response payloads even when -GoogleGenerativeAIDebugLogEnabled is not enabled. This is a port of firebase/firebase-ios-sdk#13009.

Example Error Response Log

If a responseMIMEType of application/json (JSON mode) is specified for a model that doesn't support it (e.g., gemini-1.0-pro):

[GoogleGenerativeAI] Response payload: {
  "error": {
    "code": 400,
    "message": "Json mode is not enabled for models/gemini-1.0-pro",
    "status": "INVALID_ARGUMENT"
  }
}

Updated logging to only print the NSHTTPURLResponse if -GoogleGenerativeAIDebugLogEnabled is enabled.

Example NSHTTPURLResponse Log

[GoogleGenerativeAI] The server responded with an error: <NSHTTPURLResponse: 0x600002abc760> { URL: https://generativelanguage.googleapis.com/v1beta/models/gemini-1.0-pro:generateContent } { Status Code: 400, Headers {
    "Alt-Svc" =     (
        "h3=\":443\"; ma=2592000,h3-29=\":443\"; ma=2592000"
    );
    "Cache-Control" =     (
        private
    );
    "Content-Encoding" =     (
        gzip
    );
    "Content-Length" =     (
        138
    );
    "Content-Type" =     (
        "application/json; charset=UTF-8"
    );
    Date =     (
        "Wed, 29 May 2024 14:35:12 GMT"
    );
    Server =     (
        "scaffolding on HTTPServer2"
    );
    Vary =     (
        Origin,
        "X-Origin",
        Referer
    );
    "server-timing" =     (
        "gfet4t7; dur=250"
    );
    "x-content-type-options" =     (
        nosniff
    );
    "x-frame-options" =     (
        SAMEORIGIN
    );
    "x-xss-protection" =     (
        0
    );
} }

These were swapped because the NSHTTPURLResponse is rarely useful for understanding an error on its own, whereas the response payload contains details to fix the problem.