fix(init): rename 'Custom Metrics' feature label to 'Metrics' (#659)

## Summary

- Renames the metrics feature label from "Custom Metrics" to "Metrics"
in the `sentry init` feature selection prompt
- Updates the hint text from "Track custom business metrics" to "Track
business metrics"

The "Custom" qualifier is inaccurate and doesn't match how the feature
is described elsewhere in Sentry's terminology.

Closes getsentry/cli-init-api#59

Author: MathurAditya724

src/lib/init/clack-utils.ts

@@ -43,7 +43,7 @@ const FEATURE_INFO: Record<string, { label: string; hint: string }> = {
     hint: "Code-level performance insights",
   },
   logs: { label: "Logging", hint: "Structured log ingestion" },
-  metrics: { label: "Custom Metrics", hint: "Track custom business metrics" },
+  metrics: { label: "Metrics", hint: "Track business metrics" },
   sourceMaps: {
     label: "Source Maps",
     hint: "See original source code in production errors",