Ohara: Support multiple topics in stream

[saivirtue]

In API, we accept multiple topic topicKeys for from/to fields. It is weird that we only use the *first one * as the input / output.
Currently, stream uses a "single flow" for users to define their own data flow, we need a better structure to support multiple topics.

[jackyoh]

ping @saivirtue 目前 ohara stream 是否有支援 multiple topics 的部份？因為我在改文件有看到 TODO 的字串是否可以移除此字串。

https://ohara.readthedocs.io/en/latest/rest/rest-stream.html

[vitojeng]

目前 stream 沒有支援 multiple topics, 我文件可以移除會比較好.

[jackyoh]

好，我把文件的 TODO 字串移除掉

[vitojeng]

感謝~

[chia7712]

或許可以多補充一點原因，然後議題的連結依然留著。那些閱讀到只能支持一個topic的人可能也會有相同疑惑

[jackyoh]

好，等等開會我在跟他們討論看看。

[chia7712]

等等開會我在跟他們討論看看。

痾 在議題上討論比較好

[saivirtue]

As discussed with @jackyoh and @vitojeng , I've updated the description and @jackyoh will update the doc.

[jackyoh]

Currently, stream uses a "single flow" for users to define their own data flow, we need a better structure to support multiple topics.

@saivirtue Thank you. 我就把這段話放進文件裡，後面再加上 We will support multiple topics on issue