Create separate cdn bundles for metrics

### Description

Metrics were added by accident to the base bundle in https://github.com/getsentry/sentry-javascript/pull/17883/changes

This bumps the bundle size for the error-only package unnecessarily, we should instead export this with a separate bundle like we do for tracing etc. and remove it from the base bundle.

ref https://github.com/getsentry/sentry-javascript/issues/18278