Disable async Vert.x DNS resolver when for Spring Cloud Config

 Relates to: https://groups.google.com/g/quarkus-dev/c/EJHwooQqUJE

(cherry picked from commit 75e6cfa)

extensions/spring-cloud-config-client/runtime/src/main/java/io/quarkus/spring/cloud/config/client/runtime/VertxSpringCloudConfigGateway.java

@@ -1,5 +1,7 @@
 package io.quarkus.spring.cloud.config.client.runtime;
 
+import static io.vertx.core.spi.resolver.ResolverProvider.DISABLE_DNS_RESOLVER_PROP_NAME;
+
 import java.io.ByteArrayOutputStream;
 import java.io.InputStream;
 import java.net.URI;
@@ -21,6 +23,7 @@
 import io.quarkus.runtime.TlsConfig;
 import io.quarkus.runtime.util.ClassPathUtils;
 import io.smallrye.mutiny.Uni;
+import io.vertx.core.VertxOptions;
 import io.vertx.core.net.JksOptions;
 import io.vertx.core.net.KeyStoreOptionsBase;
 import io.vertx.core.net.PfxOptions;
@@ -53,10 +56,31 @@ public VertxSpringCloudConfigGateway(SpringCloudConfigClientConfig springCloudCo
             throw new IllegalArgumentException("Value: '" + springCloudConfigClientConfig.url
                     + "' of property 'quarkus.spring-cloud-config.url' is invalid", e);
         }
-        this.vertx = Vertx.vertx();
+        this.vertx = createVertxInstance();
         this.webClient = createHttpClient(vertx, springCloudConfigClientConfig, tlsConfig);
     }
 
+    private Vertx createVertxInstance() {
+        // We must disable the async DNS resolver as it can cause issues when resolving the Vault instance.
+        // This is done using the DISABLE_DNS_RESOLVER_PROP_NAME system property.
+        // The DNS resolver used by vert.x is configured during the (synchronous) initialization.
+        // So, we just need to disable the async resolver around the Vert.x instance creation.
+        String originalValue = System.getProperty(DISABLE_DNS_RESOLVER_PROP_NAME);
+        Vertx vertx;
+        try {
+            System.setProperty(DISABLE_DNS_RESOLVER_PROP_NAME, "true");
+            vertx = Vertx.vertx(new VertxOptions());
+        } finally {
+            // Restore the original value
+            if (originalValue == null) {
+                System.clearProperty(DISABLE_DNS_RESOLVER_PROP_NAME);
+            } else {
+                System.setProperty(DISABLE_DNS_RESOLVER_PROP_NAME, originalValue);
+            }
+        }
+        return vertx;
+    }
+
     public static WebClient createHttpClient(Vertx vertx, SpringCloudConfigClientConfig springCloudConfig,
             TlsConfig tlsConfig) {