This PR extends the extensions page with support for upselling built-in
Zed features when certain keywords are searched for.
This should help inform users about features that Zed has out-of-the-box
when they go looking for them as extensions.
For example, when someone searches "vim":
<img width="1341" alt="Screenshot 2024-07-15 at 4 58 44 PM"
src="https://github.com/user-attachments/assets/b256d07a-559a-43c2-b491-3eca5bff436e">
Here are more examples of what the upsells can look like:
<img width="1341" alt="Screenshot 2024-07-15 at 4 54 39 PM"
src="https://github.com/user-attachments/assets/1f453132-ac14-4884-afc4-7c12db47ad1d">
Release Notes:
- Added banners for built-in Zed features when corresponding keywords
are used in the extension search.
