Add support for OTEL_TRACES_SAMPLER

[rads-1996]

Description

Add support for OTEL_TRACES_SAMPLER. Follows the sampler types specified in upstream opentelemetry - https://opentelemetry.io/docs/languages/sdk-configuration/general/#otel_traces_sampler in addition to the Application Insights Sampler and Rate Limited Sampler.

All SDK Contribution checklist:

• The pull request does not introduce [breaking changes]
• CHANGELOG is updated for new features, bug fixes or other significant changes.
• I have read the contribution guidelines.

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• Title of the pull request is clear and informative.
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[Copilot]

Pull request overview

This PR adds support for the OTEL_TRACES_SAMPLER environment variable, implementing standard OpenTelemetry sampler types (always_on, always_off, trace_id_ratio, and their parent-based variants) in addition to the existing Application Insights and Rate Limited samplers.

Key Changes:

• Added six new standard OpenTelemetry sampler types that can be configured via environment variables
• Implemented validation and error handling for sampler configuration parameters
• Added comprehensive test coverage for all new sampler types

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 9 comments.

Show a summary per file

File	Description
sdk/monitor/azure-monitor-opentelemetry/azure/monitor/opentelemetry/_constants.py	Defines new sampler type constants and tuple of supported samplers
sdk/monitor/azure-monitor-opentelemetry/azure/monitor/opentelemetry/_utils/configurations.py	Implements sampler configuration logic with validation and adds helper function to instantiate sampler objects
sdk/monitor/azure-monitor-opentelemetry/azure/monitor/opentelemetry/_configure.py	Integrates new sampler selection logic into tracing setup
sdk/monitor/azure-monitor-opentelemetry/tests/utils/test_configurations.py	Adds comprehensive test cases for all new sampler types and validation scenarios
sdk/monitor/azure-monitor-opentelemetry/README.md	Updates documentation to include new sampler options

[github-actions]

API Change Check

APIView identified API level changes in this PR and created the following API reviews

azure-monitor-opentelemetry

[jeremydvoss]

Disto sampling now has a lot of different and overlapping ways of configuring the sampler. Could you add one more samples to the repo?

[rads-1996]

Sure, I will include all the possible ways to set it.