Improve Task Dependency Representation

[jason810496]

• It still depends on Add Java SDK #65956 to get merged first.

What

1. Advice from Kaxil from previous JavaSDK Demo:

Any better way to list deps between tasks instead of List.of?

2. FInish the // TODO: Check duplicate key. of the following section and refine the public user interface if necessary

https://github.com/apache/airflow/pull/65956/changes#diff-a1316fe69138afea86d80cb8c2f3d1a7d7c53c229efbb3e64ee2d407fc2a3ed6R93-R98

[uranusjr]

We don’t need this for the first release since dependencies are currently represented in the stub dag instead. (Actually we should probably remove this from the initial Java SDK release. #67231)