Allow hiding unwanted sub-sections

# Feature request

Provide an option to filter/hide sub-sections/topics of documentation. This can be a toggle and/or shortcut that hides a topic (and conversely un-hide from preferences or from the Documentation's root page).

## Summary

Currently, some documentation are in-depth and contain a number of topics (for example, Terraform contains 204 topics). These topics would fill up the sidebar making it inconvenient to scroll/select through plus the content within them would also be included with searches.

Specifying a subset that we want to focus our attention on would not only increase performance but also make this tool more usable than the original sources this information is coming from.

## Examples

Using Terraform as an example, the included documentation contains 204 topics available for searching.


Usually, I would only work with a subset of platforms/providers. If I want to search for a specific subnet resource type, I can search for "subnet" through my interfaces but this returns a long list from all providers.


If I know I'm only working in OpenStack, then I will need to search for it within these results (notice it at the bottom of the list). If I was able to pre-define which topics to filter all searches and listings, I would be able to quickly identify the resource I need.

检查 issue 中描述的文档根页面、主题侧边栏、偏好设置和搜索结果。首先确定如何隐藏和恢复选定的主题子集；完成的标准是，隐藏的主题不再出现在列表或搜索结果中，同时用户可以从文档化的入口取消隐藏这些主题。

由索引模型根据 Issue 内容生成。