Configure recipients for transform notifications

Nobody has claimed this yet.

**What problem will this feature request solve?**
Currently, notifications on failed transforms are sent to all instance admins.

- Imagine I work at a 3000 people company on a team of 50 analysts. There are product analysts, and marketing analysts, and people analysts etc and they all got their own thing going on. If I'm doing product analytics, why do I care that someone's marketing transform failed? I won't even have the knowledge to fix it, I'll just keep getting spam emails that are irrelevant to me.

- Imagine I'm a metabase admin because I'm the org's infrastructure/security person. I don't know how to fix any failing transforms - I'm not a data guy! These notifications are just non-actionable noise to me.

**Describe the solution you'd like.**
Configure who gets notifications about transforms. Give people the ability to unsubscribe from specific transform notifications

**How does this feature request impact you?**
Real annoying

Start by tracing how failed transform notifications currently determine their recipients. Define the configuration and unsubscribe behavior needed for transform-specific notifications, then verify that admins no longer receive irrelevant alerts while intended recipients still do. The issue names no files or tests, so the relevant entry points must be located in the repository.

Written by the indexing model from the issue text.