[ONOS-7942] Implement k8s ingress service and watcher with unit tests

Change-Id: I8089336916e882bd31b40facf73c46c5ee541718
diff --git a/apps/k8s-networking/api/src/main/java/org/onosproject/k8snetworking/api/K8sIngressEvent.java b/apps/k8s-networking/api/src/main/java/org/onosproject/k8snetworking/api/K8sIngressEvent.java
new file mode 100644
index 0000000..c6e92fc
--- /dev/null
+++ b/apps/k8s-networking/api/src/main/java/org/onosproject/k8snetworking/api/K8sIngressEvent.java
@@ -0,0 +1,56 @@
+/*
+ * Copyright 2019-present Open Networking Foundation
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.onosproject.k8snetworking.api;
+
+import io.fabric8.kubernetes.api.model.extensions.Ingress;
+import org.onosproject.event.AbstractEvent;
+
+/**
+ * Describes kubernetes ingress event.
+ */
+public class K8sIngressEvent extends AbstractEvent<K8sIngressEvent.Type, Ingress> {
+
+    /**
+     * Creates an event of a given type for the specified kubernetes ingress.
+     *
+     * @param type      kubernetes ingress event type
+     * @param subject   kubernetes ingress
+     */
+    public K8sIngressEvent(Type type, Ingress subject) {
+        super(type, subject);
+    }
+
+    /**
+     * Kubernetes ingress events.
+     */
+    public enum Type {
+
+        /**
+         * Signifies that a new kubernetes ingress is created.
+         */
+        K8S_INGRESS_CREATED,
+
+        /**
+         *  Signifies that the kubernetes ingress is updated.
+         */
+        K8S_INGRESS_UPDATED,
+
+        /**
+         * Signifies that the kubernetes ingress is removed.
+         */
+        K8S_INGRESS_REMOVED,
+    }
+}