[java-shared-config] fmt-maven-plugin versioning

It was raised in https://github.com/googleapis/java-storage-nio/issues/1069 that the fmt-maven-plugin has moved to com.spotify.fmt

It looks like the fmt-maven-plugin dependency is [pinned to specific version](https://github.com/googleapis/java-shared-config/pull/90) due to Java 8 compatibility. I believe that would mean we can't actually depend on com.spotify.fmt instead.

Is that the case, or would there be any way to move the dependency?

If we can't change the dependency feel free to close this, just wanted to make sure it's documented!

首先检查 java-shared-config 中的 fmt-maven-plugin 依赖版本固定以及链接的 pull request 90，然后确认其版本是否受到 Java 8 兼容性的限制。将该限制与链接的 java-storage-nio issue 中引用的 com.spotify.fmt 坐标进行比较。完成的标准是记录 migration 是否可行，或确认可以关闭该 issue。

由索引模型根据 Issue 内容生成。