Fix missing cache-control when cache mactch

Signed-off-by: Bryan Frimin <bryan@getprobo.com>

pkg/server/statichandler/statichandler.go

@@ -183,6 +183,13 @@ func (s *Server) ServeSPA(w http.ResponseWriter, r *http.Request) {
 		w.Header().Set("Cache-Control", "public, max-age=3600")
 	}
 
+	if matchETag := r.Header.Get("If-None-Match"); matchETag != "" {
+		if matchETag == quotedETag {
+			w.WriteHeader(http.StatusNotModified)
+			return
+		}
+	}
+
 	http.FileServer(s.spaFS).ServeHTTP(w, r)
 }