[dynamic control] Use composable samplers and add sampler initialization

[jackshirazi]

Description:

Add initialization for TraceSamplingRatePolicy, and use the latest spec sampler (the expected future SDK default) of parent based trace ratio sampler. Note that the TraceSamplingRatePolicy installs an opinionated sampler. There can be other policies (in the future) which can be more generic, it's up to the user to choose which policy implementation they want to configure when creating the policy pipeline

Existing Issue(s):

#2546

Testing:

Added

Documentation:

Added

Outstanding items:

Wiring up the policy pipeline:

• Generic: message -> provider -> policy -> policy handler -> implementer
• eg change sampling rate message -> OpampPolicyProvider -> TraceSamplingRatePolicy -> PolicyStore -> TraceSamplingRatePolicyImplementer

Steps needed for the wiring:

• providers reading policies, eg OpampPolicyProvider, FilePolicyProvider, etc
  • DONE: OpampPolicyProvider
• implementers applying policies, eg TraceSamplingRatePolicyImplementer
  • DONE: TraceSamplingRatePolicyImplementer
• policy structures (eg TraceSamplingRatePolicy) that the provider converts messages into
  • DONE: TraceSamplingRatePolicy
• registering config to policy structures (eg "trace_sampling_rate_policy" registered to TraceSamplingRatePolicy)
• initializing policy classes (eg TraceSamplingRatePolicy needs to install a custom sampler)
  • TraceSamplingRatePolicy initialization in this PR
• activate configured providers (eg start OpampPolicyprovider reading from it's source)
• register implementers for policies (eg a new TraceSamplingRatePolicy is applied by a TraceSamplingRatePolicyImplementer)
• link the provider to processing policies and applying implementers

[Copilot]

Pull request overview

Adds runtime sampler wiring for the dynamic-control trace-sampling policy, switching sampler creation to the newer composable/parent-threshold approach.

Changes:

• Add TraceSamplingRatePolicy.initialize(...) to install a delegating sampler via autoconfigure.
• Introduce TraceSamplingRatePolicy.createSampler(probability) using composable/composite samplers.
• Update TraceSamplingRatePolicyImplementer to use createSampler(...) and log applied updates; add unit tests and incubator dependency.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
dynamic-control/src/main/java/io/opentelemetry/contrib/dynamic/policy/tracesampling/TraceSamplingRatePolicy.java	Adds initialization hook + new sampler factory using composable samplers.
dynamic-control/src/main/java/io/opentelemetry/contrib/dynamic/policy/tracesampling/TraceSamplingRatePolicyImplementer.java	Uses the new sampler factory (and logs) when applying policy changes.
dynamic-control/src/test/java/io/opentelemetry/contrib/dynamic/policy/tracesampling/TraceSamplingRatePolicyTest.java	Adds unit coverage for validation, initialization, equality/hashCode, and sampler factory behavior.
dynamic-control/build.gradle.kts	Adds incubator dependency required by the new sampler implementation.