feat: Customizing Cloudevents validation

Signed-off-by: vbhat6 <vinayas_bhat@intuit.com>

core/src/test/java/io/cloudevents/core/test/CloudEventCustomValidator.java

@@ -0,0 +1,17 @@
+package io.cloudevents.core.test;
+
+import io.cloudevents.CloudEvent;
+import io.cloudevents.core.validator.CloudEventValidator;
+
+public class CloudEventCustomValidator implements CloudEventValidator {
+
+    @Override
+    public void validate(CloudEvent cloudEvent) {
+        String namespace = null;
+        if ((namespace = (String) cloudEvent.getExtension("namespace")) != null &&
+            !namespace.equals("sales")){
+            throw new IllegalStateException("Expecting sales in namespace extension");
+        }
+    }
+
+}

core/src/test/resources/META-INF/services/io.cloudevents.core.validator.CloudEventValidator

@@ -0,0 +1 @@
+io.cloudevents.core.test.CloudEventCustomValidator