perf: auto rename attachment if it exists (#22)

Fixes halo-dev/halo#3337
不更新依赖了，直接复制了FileNameUtils
在有image.png的情况下再同时粘贴两张截图，期望两张都能被上传且被自动重命名。

![image](https://user-images.githubusercontent.com/28662535/220059741-da25a490-6f6a-4172-a393-aa3f84ab6b38.png)
![image](https://user-images.githubusercontent.com/28662535/220059786-24cda2bb-6faa-4377-8eb8-a70920916f3d.png)

```release-note
文件存在时自动重命名
```

src/main/java/run/halo/s3os/FileNameUtils.java

@@ -0,0 +1,44 @@
+package run.halo.s3os;
+
+import com.google.common.io.Files;
+import org.apache.commons.lang3.RandomStringUtils;
+import org.apache.commons.lang3.StringUtils;
+
+public final class FileNameUtils {
+
+    private FileNameUtils() {
+    }
+
+    public static String removeFileExtension(String filename, boolean removeAllExtensions) {
+        if (filename == null || filename.isEmpty()) {
+            return filename;
+        }
+        var extPattern = "(?<!^)[.]" + (removeAllExtensions ? ".*" : "[^.]*$");
+        return filename.replaceAll(extPattern, "");
+    }
+
+    /**
+     * Append random string after file name.
+     * <pre>
+     * Case 1: halo.run -> halo-xyz.run
+     * Case 2: .run -> xyz.run
+     * Case 3: halo -> halo-xyz
+     * </pre>
+     *
+     * @param filename is name of file.
+     * @param length is for generating random string with specific length.
+     * @return File name with random string.
+     */
+    public static String randomFileName(String filename, int length) {
+        var nameWithoutExt = Files.getNameWithoutExtension(filename);
+        var ext = Files.getFileExtension(filename);
+        var random = RandomStringUtils.randomAlphabetic(length).toLowerCase();
+        if (StringUtils.isBlank(nameWithoutExt)) {
+            return random + "." + ext;
+        }
+        if (StringUtils.isBlank(ext)) {
+            return nameWithoutExt + "-" + random;
+        }
+        return nameWithoutExt + "-" + random + "." + ext;
+    }
+}