Search: experiment with bool prefix query

[stsewd]

What's the problem this feature will solve?

When searching, you get results from exact words, for example if you search for "config", you don't get results from "configuration".

Describe the solution you'd like

Have a way to enable "prefix" search for a given query, similar to fuzzy search, start with a feature flag, and move it to a search time option.

We can use https://www.elastic.co/guide/en/elasticsearch/reference/current/query-dsl-match-bool-prefix-query.html and maybe complement with https://www.elastic.co/guide/en/elasticsearch/reference/7.17/index-prefixes.html to see if it improves performance, I think we can apply those changes independently.

Alternative solutions

We have fuzzy search, but it's slow, and will also return results that may not be related, since it's fuzzy!

We also have the option to use config*, but it may not be obvious to users.

Additional context

ref readthedocs/readthedocs-sphinx-search#142

We also tried to implement wildcard search a time ago, but it slowed down everything #8284.

[humitos]

We also have the option to use config*, but it may not be obvious to users.

I'd say we can implement this as the first option before jumping too deep into this feature. The new UI it's going to be more clear about what is the syntax allowed when searching. See readthedocs/addons#33

[stsewd]

I'd say we can implement this as the first option before jumping too deep into this feature.

This is already possible, we don't have to do anything, users just need to add * to their search term.