[Dynamic] Add basic Telemetry Policy support to dynamic-control

[jackshirazi]

Component(s)

dynamic-control

Is your feature request related to a problem? Please describe.

The draft Telemetry Policy seems a reasonable approach to provide a framework for dynamically updating features, so is appropriate to implement here experimentally

The current proposal provides for a process from some source of a change definition through to applying that change in the agent. At a high level, it is

• Policy Provider -> Aggregator -> Policy Implementer

An example could be

• OpAMP policy provider (reads from OpAMP) -> JSON* patch Aggregator (merges JSON for different policy types) -> Trace sampling rate Implementer (takes a new traceid rate and applies it to the sampler)

* Note JSON is the proposal in the document, and not simply an arbitrary choice for this example

Overall, the current proposal suggests these elements

FileProvider -----\
HTTPProvider ----- \  
OpAMPProvider ----- > PolicyAggregator --> PolicyStore --> PolicyImplementers
CustomProvider ----/

Describe the solution you'd like

Add in a basic example using the proposed framework, to periodically read from a file and applying it to dynamically changing the sampling rate. Expected additions:

• TelemetryPolicy
• PolicyProvider interface for providers common behaviours
• LinePerPolicyFileProvider to read a file and create TelemetryPolicys
• PolicyAggregator to merge TelemetryPolicys - for flat files this is overkill but for structured files, the result is needed
• PolicyImplementer interface to handle changes to policies, so that the ...
• PolicyStore handles changes and propagates them to appliers
• A DelegatingSampler so that changes can be applied generically in the sampler chain
• A specific TraceSamplingRatePolicyImplementer to apply changes to the sampling rate
• env var/property/config option to specify a flat file
• A TelemetryPolicyManager which manages the full process
• extension handling so that this can be used as an extension

To keep things easy for reviews, I'll add things piecewise. A full working implementation is here in this branch.

Describe alternatives you've considered

No response

Additional context

Part of #2416

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