Add built-in deny policy documentation

docs/docs/user_docs/dev_manual/blocking-queue-custom.md

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 # 阻塞队列自定义

docs/docs/user_docs/dev_manual/rejected-policy-custom.md

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 # 拒绝策略自定义

docs/docs/user_docs/dev_manual/rejected-policy-info.md

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+
+# 内置拒绝策略
+
+内置两种拒绝策略说明：
+
+**RunsOldestTaskPolicy**：添加新任务并由主线程运行最早的任务。
+
+```java
+public class RunsOldestTaskPolicy implements RejectedExecutionHandler {
+
+    @Override
+    public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
+        if (executor.isShutdown()) {
+            return;
+        }
+        BlockingQueue<Runnable> workQueue = executor.getQueue();
+        Runnable firstWork = workQueue.poll();
+        boolean newTaskAdd = workQueue.offer(r);
+        if (firstWork != null) {
+            firstWork.run();
+        }
+        if (!newTaskAdd) {
+            executor.execute(r);
+        }
+    }
+}
+```
+
+**SyncPutQueuePolicy**：主线程把拒绝任务以阻塞的方式添加到队列。
+
+```java
+@Slf4j
+public class SyncPutQueuePolicy implements RejectedExecutionHandler {
+
+    @Override
+    public void rejectedExecution(Runnable r, ThreadPoolExecutor executor) {
+        if (executor.isShutdown()) {
+            return;
+        }
+        try {
+            executor.getQueue().put(r);
+        } catch (InterruptedException e) {
+            log.error("Adding Queue task to thread pool failed.", e);
+        }
+    }
+}
+```