Use HTTP/1.1 to perform readiness check (#156)

This change re-enables the readiness check, using HTTP/1.1 instead of
HTTP/2 to invoke it. The readiness checks are unauthenticated and are
throttled when the feature gate UnauthenticatedHTTP2DOSMitigation is set
to true, which is the default starting in Kubernetes 1.29 (see
https://kubernetes.io/docs/reference/command-line-tools-reference/feature-gates).
This was the cause of the "GOAWAY received" errors that have been
observed on Kubernetes 1.29.

This change also decouples starting of the servers from waiting until
they become ready, so that if the readiness check fails due to some
error that propagates out of the polling loop (e.g. IOException), the
caller is free to catch it and continue waiting.

core/src/main/java/io/javaoperatorsdk/jenvtest/process/KubeAPIServerProcess.java

@@ -89,9 +89,7 @@ public void waitUntilReady() {
     var readinessChecker = new ProcessReadinessChecker();
     var timeout = config.getStartupTimeout();
     var startTime = System.currentTimeMillis();
-    // the 1.29.0 binary has issue with this. Will temporarily comment out and further investigate.
-    // But with this now all the executions are failing
-    // readinessChecker.waitUntilReady(apiServerPort, "readyz", KUBE_API_SERVER, true, timeout);
+    readinessChecker.waitUntilReady(apiServerPort, "readyz", KUBE_API_SERVER, true, timeout);
     int newTimout = (int) (timeout - (System.currentTimeMillis() - startTime));
     readinessChecker.waitUntilDefaultNamespaceAvailable(apiServerPort, binaryManager, certManager,
         config, newTimout);

core/src/main/java/io/javaoperatorsdk/jenvtest/process/ProcessReadinessChecker.java

@@ -177,8 +177,13 @@ public void checkServerTrusted(
               }
           },
           null);
+      // Set protocol to HTTP/1.1 for unauthenticated invocations of "GET /readyz". Sending
+      // unauthenticated requests using HTTP/2 is problematic on Kubernetes >=1.29, which enables
+      // denial-of-service mitigation for authenticated HTTP/2 by default with the
+      // UnauthenticatedHTTP2DOSMitigation feature gate.
       return HttpClient.newBuilder()
           .sslContext(sslContext)
+          .version(HttpClient.Version.HTTP_1_1)
           .build();
     } catch (NoSuchAlgorithmException | KeyManagementException e) {
       throw new JenvtestException(e);