tests/e2e: add HTTP response cache e2e tests

tests/e2e/scripts/http_cache_backend.py

@@ -0,0 +1,20 @@
+from http.server import BaseHTTPRequestHandler, HTTPServer
+
+_counter = 0
+
+
+class Handler(BaseHTTPRequestHandler):
+    def do_GET(self):
+        global _counter
+        _counter += 1
+        body = b"cache-test-%d" % _counter
+        self.send_response(200)
+        self.send_header("Content-Length", str(len(body)))
+        self.end_headers()
+        self.wfile.write(body)
+
+    def log_message(self, format, *args):
+        return
+
+
+HTTPServer(("0.0.0.0", 5677), Handler).serve_forever()