Implement Sampling Seed Propagation

[mydea]

Description

See https://develop.sentry.dev/sdk/telemetry/traces/#propagated-random-value

We want to implement Sampling Seed Propagation, so all SDKs use the same random seed inside of a trace.

[lforst]

To do for this issue:

• Only pass root spans through sampling pipeline (feat(opentelemetry)!: Exclusively pass root spans through sampling pipeline #14951)
• Propagate a sampling random (feat: Propagate and use a sampling random #14989)
• Pass parentSampleRate to tracesSampler (feat: Pass parentSampleRate to tracesSampler #15024)
• Document how to properly use tracesSampler