feat: introduce backend url environment variable

ref: N25B-352

src/config/api.ts

@@ -0,0 +1,11 @@
+declare const __VITE_API_BASE_URL__: string | undefined;
+
+const DEFAULT_API_BASE_URL = "http://localhost:8000";
+
+const rawApiBaseUrl =
+  (typeof __VITE_API_BASE_URL__ !== "undefined" ? __VITE_API_BASE_URL__ : undefined) ??
+  DEFAULT_API_BASE_URL;
+
+export const API_BASE_URL = rawApiBaseUrl.endsWith("/")
+  ? rawApiBaseUrl.slice(0, -1)
+  : rawApiBaseUrl;