fix(middleware): define middleware in a more streamlined way

middleware/content_security_policiy.go

@@ -5,6 +5,8 @@ import "net/http"
 func ContentSecurityPolicy(next http.Handler) http.Handler {
 
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		// While this value can be overridden, it can't be moved to after the next.ServeHTTP call,
+		// because if the response writer get's closed, the headers can't be set anymore
 		w.Header().Set("Content-Security-Policy", "default-src 'self' https://umami.me-fit.eu")
 
 		next.ServeHTTP(w, r)