docs: upgrade gatsby theme & format docs

[BBSQQ]

升级官网版本，整理 doc 规范表达

• 统一 en 下标题（首字母大写，其他小写（标题是单词首字母大写），不用 chart 用 plot）
• 统一 description 表述配置项内容（ optional number default 400）
• 补齐 manual 部分缺失图表文档
• 统一 examples 部分统一引用 docs 部分文档

已经升级到了可用版本，接下来大家走查一下文档和 demo 的情况，没问题就可以部署了

[github-actions]

🎊 PR Preview 5b59048 has been successfully built and deployed to https://antvis-G2Plot-preview-pr-1835.surge.sh

🕐 Build time: 619.178s

_{🤖 By surge-preview}

[BBSQQ]

@lxfu1 官网升级版本了，可以走查了

[coveralls]

Pull Request Test Coverage Report for Build 341642669

• 0 of 0 changed or added relevant lines in 0 files are covered.
• 21 unchanged lines in 7 files lost coverage.
• Overall coverage increased (+0.08%) to 93.335%

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Files with Coverage Reduction	New Missed Lines	%
src/core/plot.ts	1	97.48%
src/plots/sunburst/adaptor.ts	1	95.83%
src/plots/column/adaptor.ts	2	91.43%
src/plots/scatter/adaptor.ts	2	88.46%
src/plots/histogram/adaptor.ts	3	85.71%
src/adaptor/conversion-tag.ts	6	83.33%
src/plots/pie/label/inner-label.ts	6	35.0%

Totals
Change from base Build 337570953:	0.08%
Covered Lines:	3584
Relevant Lines:	3698

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💛 - Coveralls