feat(alerts): choose which environments an alert applies to

See related MR: glitchtip-backend!2503 (merged)

Summary

It adds environment-based filtering for a project for alerts - frontend part.

Testing

I created a local instance of Glitchtip, used curl to inject new errors. On a separate console tab, I watched the results, I could verify that only production environment fires alters. See the screencast.

AI disclosure: feature drafted with AI, tested by hand

• I am respecting Sentry's proprietary Business Source License (BSL) by implementing code in a clean room environment. I have not read any BSL Sentry code. It is OK to read MIT licensed code.