Publish html_to_markdown (#13718)

This PR updates the `html_to_markdown` crate with the necessary changes
to publish it to crates.io.

Publishing it makes it available for use within extensions when
implementing functionality for the Assistant.

Release Notes:

- N/A

crates/html_to_markdown/src/html_to_markdown.rs

@@ -1,4 +1,4 @@
-//! Provides conversion from rustdoc's HTML output to Markdown.
+//! Convert HTML to Markdown.
 
 mod html_element;
 pub mod markdown;