fix(node-experimental): Sample in OTEL Sampler

[mydea]

In order for sampling propagation to work, we need to sample in OTEL, not in Sentry. As the sentry spans are only created later.

This actually also means we can remove the sampleTransaction export from core again 🎉 (I'll remove this export in a separate PR, this has not been released yet).

Note that this does not fix propagation yet in node-experimental, once this is merged I still need to adjust the propagator (or rather, fork it) from opentelemetry-node to work without sentry spans.

[github-actions]

size-limit report 📦

Path	Size
@sentry/browser (incl. Tracing, Replay) - Webpack (gzipped)	84.22 KB (-0.03% 🔽)
@sentry/browser (incl. Tracing) - Webpack (gzipped)	31.41 KB (0%)
@sentry/browser - Webpack (gzipped)	22 KB (0%)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (gzipped)	78.77 KB (+0.02% 🔺)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (gzipped)	28.6 KB (+0.04% 🔺)
@sentry/browser - ES6 CDN Bundle (gzipped)	21.01 KB (+0.05% 🔺)
@sentry/browser (incl. Tracing, Replay) - ES6 CDN Bundle (minified & uncompressed)	254.47 KB (+0.04% 🔺)
@sentry/browser (incl. Tracing) - ES6 CDN Bundle (minified & uncompressed)	86.75 KB (+0.11% 🔺)
@sentry/browser - ES6 CDN Bundle (minified & uncompressed)	62.44 KB (+0.16% 🔺)
@sentry/browser (incl. Tracing) - ES5 CDN Bundle (gzipped)	31.46 KB (+0.04% 🔺)
@sentry/react (incl. Tracing, Replay) - Webpack (gzipped)	84.25 KB (-0.03% 🔽)
@sentry/react - Webpack (gzipped)	22.05 KB (0%)
@sentry/nextjs Client (incl. Tracing, Replay) - Webpack (gzipped)	102.22 KB (-0.02% 🔽)
@sentry/nextjs Client - Webpack (gzipped)	50.99 KB (-0.01% 🔽)

[lforst]

sound!