[4.2.3 RTC] Release Notes + API ref

[Cilla-luodan]

Hi, The docs for v4.2.3 are ready, please see this tag for the release notes and API ref: https://github.com/AgoraIO/agora_doc_source/releases/tag/v4.2.2

• The diff of the ditamaps is in this url: https://github.com/AgoraIO/agora_doc_source/compare/v4.2.2...v4.2.3#diff-699d5932fe62f565999f0154f0362af4be7fdaf010a3873301f25424bd2a158e
• The release notes are in the old place: markdown/RTC 4.x/release-notes/en-US

Here're some notes for this release:

1. Don't be frightened by the huge diff of the ditamaps, this is because we have update the structure of the CN API ref. The change scope of v4.2.3 is quite small.
2. Starting from this version, we no longer provide separate release notes for video SDK and audio SDK. They're represented on the CN doc site as the Interactive SDK. If you still want to have two different sets of release notes, please remove the video-related content from the current release notes and create a separate set of audio release notes for the audio SDK.

[Cilla-luodan]

There's a known issue of Android that needs to be added in the release notes, pls see this tag for updates: https://github.com/AgoraIO/agora_doc_source/releases/tag/v4.2.3-1011

The release notes of Android, RN, Unity, and Flutter also need to be updated, do the necessary editing as your need.