sphinxdocs: i18n support

# sphinxdocs: i18n support

### Relevant Rules

`sphinx_docs` in `//sphinxdocs/sphinxdocs/sphinx.bzl`

### Description

`sphinx_docs` should accept a `lang` array of strings and produce docs for each specified language

### Describe the solution you'd like

per https://www.sphinx-doc.org/en/master/usage/advanced/intl.html I think it would have to run `sphinx-build gettext`, save the `.po` files somewhere within the repo (pretty sure that these are checked into the VCS), and then run `sphinx-build -Dlanguage=` for every specified lang

### Describe alternatives you've considered

`sphinx-intl` seems to be the common extension for i18n workflows but it doesn't seem strictly required https://www.sphinx-doc.org/en/master/usage/advanced/intl.html#translating-with-sphinx-intl

首先阅读 `//sphinxdocs/sphinxdocs/sphinx.bzl` 中的 `sphinx_docs` 规则以及链接的 Sphinx 国际化工作流。完成的标准是该规则接受 `lang` 数组，按需生成翻译文件，并为每种指定的语言生成文档。

由索引模型根据 Issue 内容生成。