Add a prometheus exporter

Change-Id: I2989d87c2a83eed31c6617694bdcb78bf9b38553
diff --git a/apps/openstacktelemetry/api/src/main/java/org/onosproject/openstacktelemetry/api/config/PrometheusTelemetryConfig.java b/apps/openstacktelemetry/api/src/main/java/org/onosproject/openstacktelemetry/api/config/PrometheusTelemetryConfig.java
new file mode 100644
index 0000000..536bd53
--- /dev/null
+++ b/apps/openstacktelemetry/api/src/main/java/org/onosproject/openstacktelemetry/api/config/PrometheusTelemetryConfig.java
@@ -0,0 +1,82 @@
+/*
+ * Copyright 2018-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.openstacktelemetry.api.config;
+
+import java.util.Map;
+
+public interface PrometheusTelemetryConfig extends TelemetryConfig {
+
+    /**
+     * Obtains prometheus exporter IP address.
+     *
+     * @return IP address which prometheus exporter binds
+     */
+    String address();
+
+    /**
+     * Obtains prometheus exporter port number.
+     *
+     * @return prometheus exporter port number
+     */
+    int port();
+
+    /**
+     * Obtains prometheus config maps.
+     *
+     * @return prometheus config map
+     */
+    Map<String, Object> configMap();
+
+
+    /**
+     * Builder class of PrometheusTelemetryConfig.
+     */
+    interface Builder extends TelemetryConfig.Builder {
+
+        /**
+         * Sets prometheus exporter IP address.
+         *
+         * @param address prometheus exporter IP
+         * @return builder instance
+         */
+        Builder withAddress(String address);
+
+        /**
+         * Sets prometheus exporter port number.
+         *
+         * @param port prometheus exporter port
+         * @return builder instance
+         */
+        Builder withPort(int port);
+
+        // TODO   add authentication.
+
+        /**
+         * Sets other prometheus configuration map.
+         *
+         * @param configMap prometheus configuration map
+         * @return builder instance
+         */
+        Builder withConfigMap(Map<String, Object> configMap);
+
+        /**
+         * Creates a prometheus telemetry config instance.
+         *
+         * @return prometheus telemetry config instance
+         */
+        PrometheusTelemetryConfig build();
+    }
+}