feat(core): Streamline custom hub creation for node-experimental

[mydea]

This is an intermediate step to streamline what we need to customize in OTEL. This should make it easier to slowly remove customizations there.

The main change is that you can set a createHub method on the main carrier, which will be used if set. This way, all the code we have to duplicate in node-experimental right now just to create the correct OpenTelemetryHub can mostly go away.

We will remove this again during then v8 cycle.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser (incl. Tracing, Replay, Feedback) - Webpack (gzipped)	78.34 KB (+0.02% 🔺)
@sentry/browser (incl. Tracing, Replay) - Webpack (gzipped)	69.55 KB (-0.02% 🔽)
@sentry/browser (incl. Tracing, Replay with Canvas) - Webpack (gzipped)	73.5 KB (+0.01% 🔺)
@sentry/browser (incl. Tracing, Replay) - Webpack with treeshaking flags (gzipped)	63.19 KB (+0.02% 🔺)
@sentry/browser (incl. Tracing) - Webpack (gzipped)	33.54 KB (+0.05% 🔺)
@sentry/browser (incl. browserTracingIntegration) - Webpack (gzipped)	33.4 KB (+0.06% 🔺)
@sentry/browser (incl. Feedback) - Webpack (gzipped)	31.39 KB (+0.07% 🔺)
@sentry/browser (incl. sendFeedback) - Webpack (gzipped)	31.39 KB (+0.07% 🔺)
@sentry/browser - Webpack (gzipped)	22.65 KB (+0.07% 🔺)
@sentry/browser (incl. Tracing, Replay, Feedback) - ES6 CDN Bundle (gzipped)	76.37 KB (+0.02% 🔺)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (gzipped)	67.9 KB (0%)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (gzipped)	33.67 KB (+0.03% 🔺)
@sentry/browser - ES6 CDN Bundle (gzipped)	24.74 KB (+0.02% 🔺)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (minified & uncompressed)	214.09 KB (+0.01% 🔺)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (minified & uncompressed)	101.89 KB (+0.02% 🔺)
@sentry/browser - ES6 CDN Bundle (minified & uncompressed)	74.27 KB (+0.02% 🔺)
@sentry/browser (incl. Tracing) - ES5 CDN Bundle (gzipped)	36.82 KB (+0.06% 🔺)
@sentry/react (incl. Tracing, Replay) - Webpack (gzipped)	69.95 KB (+0.03% 🔺)
@sentry/react - Webpack (gzipped)	22.68 KB (+0.05% 🔺)
@sentry/nextjs Client (incl. Tracing, Replay) - Webpack (gzipped)	87.55 KB (+0.01% 🔺)
@sentry/nextjs Client - Webpack (gzipped)	51.73 KB (+0.02% 🔺)
@sentry-internal/feedback - Webpack (gzipped)	17.23 KB (+0.08% 🔺)