[Docs] Add upgrade notes for fluss package changes

[wuchong]

Search before asking

• I searched in the issues and found nothing similar.

Description

The 0.8 uses new groupId and package org.apache.fluss, the 0.7 uses legacy com.alibaba.fluss. This is a breaking change for Java clients users and should be listed in the upgrade notes.

Willingness to contribute

• I'm willing to submit a PR!

[caozhen1937]

Hi @wuchong , is anyone working on this task? If not, can you assign it to me?