Notify user when a new identity is linked or removed from their account

### Problem Statement Currently, in Sentry, when a user links a new Identity or removes an identity (ex. Discord, Google, Slack, etc) to their account there is no email notification. Linked identities can be found under `/settings/account/identities/`. ### Solution Brainstorm Send an email notification to the primary verified email on the account regarding the identity linking/removal. ### Product Area Settings - Auth We want to define a set of [lightweight metrics](<https://docs.sentry.io/product/explore/metrics/>) that SDKs can automatically collect for e.g. framework, language or platform, focusing only on signals that **do NOT overlap with Tracing**. Ideally these metrics should give a quick sense of app or runtime health, … while deeper investigation will still rely on traces or profiles.<br><br>Examples**:** * Node.js runtime metrics (e.g., event loop delay, heap usage) * Prisma-related metrics in Next.js * Mobile CPU / memory usage to help surface potential ANRs or app hangs --- **Candidate Metrics (add more below)** * … *(please also add ideas, questions or examples in comments)*