PMD upgrade to 7.x

## Pull request overview

Bumps the Maven PMD plugin version used by the build from 3.12.0 to 3.28.0.

**Changes:**
- Update `cs.pmd-plugin.version` property to `3.28.0`.

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_Originally posted by @Copilot in https://github.com/apache/cloudstack/pull/12543#pullrequestreview-3735812711_

找到包含 `cs.pmd-plugin.version` 属性的 Maven 构建配置，并确认其当前值。将其从 3.12.0 更新为 3.28.0，然后运行相关的 Maven 构建或 PMD 检查；当构建使用所请求的插件版本且没有出现新的失败时，即表示完成。

由索引模型根据 Issue 内容生成。