Refactor API providers

[sashabaranov]

We have a growing number of different API providers: OpenAI, Azure, Cloudflare Getaway. At the same time other tools keep adding their OpenAI-compatible APIs (e.g. Ollama).

Considering #693, here's a sketch of how we can add new API providers painlessly:

type apiProvider interface { // might want to expose that
	SetAuthForRequest(req *http.Request)
	GetFullURL(suffix string, args ...any) // Shouldn't be `any`, but a type-safe list like requestOption
}

type APIProviderConfig interface {
	// whatever we need here
}

client usage:

config := openai.DefaultConfigWithAPIProvider(
	openai.AzureOpenAIProviderConfig("your Azure OpenAI Key", "https://your Azure OpenAI Endpoint"),
)
client := openai.NewClientWithConfig(config)

[qingdi]

your kind, Cloudflare how to do ?

[sashabaranov]

@qingdi pretty much the same!

config := openai.DefaultConfigWithAPIProvider(
	openai.CloudflareProviderConfig(...),
)
client := openai.NewClientWithConfig(config)