关于dubbo-bom 的作用

- [ ] I have searched the [issues](https://github.com/apache/dubbo/issues) of this repository and believe that this is not a duplicate.

## Ask your question here
关于 dubbo-dependencies-bom 的疑问：
1、dubbo-samples里面引用了 dubbo-bom
https://github.com/apache/dubbo-samples/blob/master/dubbo-samples-spring-boot/pom.xml

3、实际上
项目里面用dubbo的话，引用的应该是这个
`

org.apache.dubbo
dubbo
${dubbo.version}
`

Start with the referenced dubbo-samples-spring-boot/pom.xml and compare its dubbo-bom usage with the dependency declaration shown in the issue. Trace the relevant BOM and dependency-management references in the repository, then document their intended roles and when each should be used. Done means the distinction is explained clearly with an accurate example.

Written by the indexing model from the issue text.