assistant: Add basic glob support for expanding items in `/docs` (#14370)

This PR updates the `/docs` slash command with basic globbing support
for expanding docs.

A `*` can be added to the item path to signify the end of a prefix
match.

For example:

```
# This will match any documentation items starting with `auk::`.
# In this case, it will pull in the docs for each item in the crate.
/docs docs-rs auk::*

# This will match any documentation items starting with `auk::visitor::`,
# which will pull in docs for the `visitor` module.
/docs docs-rs auk::visitor::*
```


https://github.com/user-attachments/assets/5e1e21f1-241b-483f-9cd1-facc3aa76365

Release Notes:

- N/A