danger: Check PR titles (#13053)

This PR sets up Danger to check PR titles for consistency, using
[`danger-plugin-pr-hygiene`](https://github.com/maxdeviant/danger-plugin-pr-hygiene).

<img width="919" alt="Screenshot 2024-06-14 at 11 16 31 AM"
src="https://github.com/zed-industries/zed/assets/1486634/167fe698-2505-422b-8e41-e121d9fe933f">

Release Notes:

- N/A