[dynamic control] Add pipeline config initialization from file

[jackshirazi]

Description:

Adding a method to read a pipeline initialization file in yaml (preferred) or json format.

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:

• configuring the pipeline
  • DONE in this PR
• 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)
  • DONE TraceSamplingRatePolicy initialization
• 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 support in the dynamic-control module to initialize the policy pipeline configuration from an external YAML (preferred) or JSON file, selected via OpenTelemetry ConfigProperties.

Changes:

• Added PolicyInitConfig.readFromConfigProperties(ConfigProperties) to load init configuration from a YAML/JSON file path configured via properties.
• Added unit tests covering YAML-vs-JSON precedence, fallback when YAML property is blank, and failure scenarios (missing/unparseable files).

Reviewed changes

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

File	Description
dynamic-control/src/main/java/io/opentelemetry/contrib/dynamic/policy/registry/PolicyInitConfig.java	Adds config-property driven file loading (YAML preferred, JSON supported) with logging on failure.
dynamic-control/src/test/java/io/opentelemetry/contrib/dynamic/policy/registry/PolicyInitConfigTest.java	Adds coverage for selection logic and error handling behavior.