feat: Create startup proxy service and interface

Resolves #28 (closed)

core/src/main/java/org/eclipsefoundation/core/service/StartupProxy.java

+/*********************************************************************
+* Copyright (c) 2022 Eclipse Foundation.
+*
+* This program and the accompanying materials are made
+* available under the terms of the Eclipse Public License 2.0
+* which is available at https://www.eclipse.org/legal/epl-2.0/
+*
+* Author: Zachary Sabourin <zachary.sabourin@eclipse-foundation.org>
+*
+* SPDX-License-Identifier: EPL-2.0
+**********************************************************************/
+package org.eclipsefoundation.core.service;
+
+import org.slf4j.Logger;
+import org.slf4j.LoggerFactory;
+
+/**
+ * Allows beans to get picked up by the StartupProxyService. The desired class
+ * must extend this interface.
+ */
+public interface StartupProxy {
+    static final Logger LOGGER = LoggerFactory.getLogger(StartupProxy.class);
+
+    default void startupProxy() {
+        LOGGER.info("{} bean initialized in startup phase", getClass().getSimpleName());
+    }
+}