Customizable email subject for Uptime alerts

### Problem Statement We use Sentry Uptime monitoring and rely a lot on email alerts for day-to-day operations. Right now, the email subject for Uptime alerts is fixed, which makes it hard to set up reliable inbox filters—especially when you’re dealing with multiple environments, services, or teams. Because of this, alerts often end up mixed together in the inbox and require manual sorting, which adds noise and slows down response time for on-call engineers. ### Solution Brainstorm It would be really helpful if the email subject for Uptime alerts could be customized in some way. For example: - Allow a custom subject or subject template - Support simple variables like project, environment, status This would make it much easier to filter, route, and prioritize alerts using standard email rules. ### Product Area Other