[Doc] Add guides for Transactions

[Anonymitaet]

Pulsar 2.8 has been released and one of the highlights is transaction API, which supports atomic writes and acknowledgments across multiple topics. It completes our vision of making Pulsar a complete unified messaging and streaming platform.

While the previous transaction docs are incomplete and need to be improved, so I've re-architectured it and added missing contents.

This PR fixes #10971 and it is based on the google doc I collaborated with @congbobo184 and @D-2-Ed, so it should be pretty good already.

[Anonymitaet]

@congbobo184 @jennifer88huang @Huanli-Meng could you please help review? Many thanks

[congbobo184]

LGTM.

[lhotari]

LGTM.

I wonder if the Pulsar binary protocol specification https://pulsar.apache.org/docs/en/develop-binary-protocol/ / https://github.com/apache/pulsar/blob/master/site2/docs/developing-binary-protocol.md needs updating to make it consistent with transactions? Any ideas how to cover that?

[Anonymitaet]

Hi @lhotari thanks for your feedback.

I've discussed w/ @congbobo184, we are considering making the following changes to doc:

1. Add transaction section under the interactions chapter
   

2. Add descriptions for transaction command in the source code file (rather than in user guide) and add links of the source code file to the user guide.

Reason:

• The descriptions are simple.
• Developers make code changes at any time or frequently (for example, add a transaction command), it is not easy to capture all code changes and sync doc with code. But we provide the source code file link, so that users can be navigated to the source code file to get the latest and complete info.

3. Add a diagram (something like below) of transaction to the user guide.

Any thoughts?

[Anonymitaet]

Hi @lhotari any feedback?