add cache with time-to-live for unauthed GH API call

src/codegate/api/v1_processing.py

@@ -4,6 +4,7 @@
 from collections import defaultdict
 from typing import AsyncGenerator, Dict, List, Optional, Tuple
 
+import cachetools.func
 import requests
 import structlog
 
@@ -31,6 +32,7 @@
 ]
 
 
+@cachetools.func.ttl_cache(maxsize=128, ttl=20 * 60)
 def fetch_latest_version() -> str:
     url = "https://api.github.com/repos/stacklok/codegate/releases/latest"
     headers = {"Accept": "application/vnd.github+json", "X-GitHub-Api-Version": "2022-11-28"}