website: improve search - do not show <code> tags in results

[alexandear]

When searching for linters.fast on the website, the search results display the raw HTML tag <code>linters.fast</code> instead of the plain text.

The search index should strip HTML tags so that results show only the readable text content.

[ldez]

This is related to the theme: the search engine inside the theme is handling that.
I've worked on improvements on this search engine in the past, and the implementation is not easy to improve.

Inside golangci-lint documentation, we cannot change that.