[Discord] Support issue alerts over direct message

Not sure how best to support this. Perhaps a drop down to select channel or user in the alert creation menu? On the backend things should be pretty similar to server channels. DM's are also considered channels and have a channel ID, but we may need to make an extra request to create the DM channel with a specific user. Note that it might even be possible to use Discord usernames. 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)*