feat: Update endpoint countries

endpoints/countries.get.py

@@ -0,0 +1,8 @@
+from fastapi import FastAPI
+from typing import List
+
+app = FastAPI()
+
+@app.get("/countries", response_model=List[str])
+def get_countries():
+    return ["USA", "Canada", "Germany", "France", "Japan", "Australia"]