Added changes for rate limited sampler (azure-distro changes)

[rads-1996]

Description

Adding support for RateLimitedSampler, inspired by Java Application Insights sampler
https://github.com/microsoft/ApplicationInsights-Java/blob/main/agent/agent-tooling/src/main/java/com/microsoft/applicationinsights/agent/internal/sampling/RateLimitedSamplingPercentage.java

This PR contains changes related to the configurations in the azure-distro only. The changes related to implementation of the rate limited sampler are in the azure-exporter in the PR - #41954.

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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Testing Guidelines

• Pull request includes test coverage for the included changes.

[Copilot]

Pull Request Overview

This PR extends the azure-distro to let users choose between a fixed‐percentage and a rate‐limited traces sampler via OTEL environment variables. Key changes include:

• Parsing OTEL_TRACES_SAMPLER (sampler type) and OTEL_TRACES_SAMPLER_ARG (its argument) in _get_configurations.
• Adding new constants (RATE_LIMITED_SAMPLER, FIXED_PERCENTAGE_SAMPLER, SAMPLING_TRACES_PER_SECOND_ARG) and updating azure/monitor/opentelemetry/_constants.py.
• Updating _configure.py to select RateLimitedSampler when sampling_traces_per_second is set.

Reviewed Changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 4 comments.

Show a summary per file

File	Description
.../tests/utils/test_configurations.py	Replaced SAMPLING_RATIO_ENV_VAR, added rate‐limited and fixed tests
.../azure/monitor/opentelemetry/_utils/configurations.py	Updated sampling defaults to branch on sampler type and argument
.../azure/monitor/opentelemetry/_constants.py	Introduced new constants for sampler types and trace‐per‐second arg
.../azure/monitor/opentelemetry/_configure.py	Added logic to wire up RateLimitedSampler when appropriate
...-exporter/tests/trace/test_rate_limited_sampling.py	New comprehensive tests for RateLimitedSampler
...-exporter/azure/.../_utils.py	Added _get_djb2_sample_score and rounding helper
...-exporter/azure/.../_rate_limited_sampling.py	Implemented RateLimitedSamplingPercentage and RateLimitedSampler

Comments suppressed due to low confidence (2)

sdk/monitor/azure-monitor-opentelemetry/tests/utils/test_configurations.py:178

• This test sets an invalid sampler arg ("Half") but does not assert that sampling_ratio falls back to the default. Consider adding an assertion such as self.assertEqual(configurations["sampling_ratio"], 1.0) to verify fallback behavior.

    @patch.dict(

sdk/monitor/azure-monitor-opentelemetry-exporter/azure/monitor/opentelemetry/exporter/export/trace/_utils.py:330

• No tests cover _round_down_to_nearest or edge cases of _get_djb2_sample_score. Adding unit tests would improve confidence in these utility functions.

def _get_djb2_sample_score(trace_id_hex: str) -> float:

[hectorhdzg]

We should bump to 1.7.0 because of new features