Subscribe to new issues in a release

## Summary

A user can subscribe to notifications of new issues that appear in a specific release.

## Motivation

We have (and I think this is a pretty common scenario) a project in Sentry with a large volume of errors in it. When we put out a new deployment, we often find ourselves watching the "New Issues" tab on the associated Sentry Release and refreshing for a little while. It would be great if we could instead tell the Release to notify us if there's a new issue that appears.

## Additional Context

I imagine a potential user experience for this could be a button on the release page that can be clicked to subscribe to, looking like this:


It would also be useful to be able to subscribe a user programmatically with the sentry CLI, since we could then automatically subscribe people when they issue a deploy.