docs/zh_CN: Add subsystem-apis Chinese translation

Translate subsystem-apis.rst into Chinese.

The existence of this document is crucial. Without it, other Chinese
documents included in (such as sched-design-CFS.rst) will not be
displayed correctly in the left side of the web page.

Signed-off-by: Tang Yizhou <yizhou.tang@shopee.com>
Reviewed-by: Yanteng Si <siyanteng@loongson.cn>
Signed-off-by: Jonathan Corbet <corbet@lwn.net>
Message-ID: <20231011152520.31079-1-tangyeechou@gmail.com>