feat: Allow customization of OpenAI host with environment variable (#152)

This commit modifies the OpenAI host configuration to support customization through an environment variable. This change is particularly useful in scenarios where access to the official OpenAI host is restricted or unavailable, allowing users to configure an alternative host for their specific needs.

pages/api/models.ts

@@ -1,4 +1,5 @@
 import { OpenAIModel, OpenAIModelID, OpenAIModels } from "@/types";
+import { OPENAI_API_HOST } from "@/utils/app/const";
 
 export const config = {
   runtime: "edge"
@@ -10,7 +11,7 @@ const handler = async (req: Request): Promise<Response> => {
       key: string;
     };
 
-    const response = await fetch("https://api.openai.com/v1/models", {
+    const response = await fetch(`${OPENAI_API_HOST}/v1/models`, {
       headers: {
         "Content-Type": "application/json",
         Authorization: `Bearer ${key ? key : process.env.OPENAI_API_KEY}`