Filter documentation via a query parameter for better browser interoperability

# Feature request
Filter documentation via an optional query parameter

## Summary
DevDocs makes it really easy to filter on a specific set of docs in the UI, which is great. I use this in conjunction with browser site search to pass queries directly to the DevDocs search endpoint to skip landing on the main page first. However, there is one disadvantage: I can't seem to filter the documentation from the search endpoint directly. If want to search for a ruby-specific method from site search, I need to land on the main DevDocs page and filter manually.

[Browsers are embracing custom site search functionality](https://resources.arc.net/en/articles/7183263-site-search-directly-search-any-website) to allow quick access to search endpoints that can be invoked via a shortcut and this has become an important part of my workflow. It would be great to have documentation filtering in the search API to improve the interoperability of DevDocs search.

## Examples

The query endpoint looks like this:

`https://devdocs.io/#q=%s` where `%s` is replaced with my query string

It would be great to be able to do something like this to search only within Ruby 3.1:
`https://devdocs.io/#q=%s&doc=ruby3-1`

Bắt đầu từ endpoint truy vấn DevDocs được nêu trong issue, https://devdocs.io/#q=%s, và theo dõi cách trình duyệt xử lý tham số q cũng như việc lọc tài liệu. Hoàn thành khi một URL có thể chứa doc=ruby3-1 để việc tìm kiếm chỉ được thực hiện trên bộ tài liệu được yêu cầu.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.