[AzureMonitorExporter] [AzureMonitorDistro] Change default to rate limited sampler without api change

[harsimar]

This PR changes the default sampler to rate limited. When we choose to do a major version bump, we will consider changing this implementation to have a nullable sample ratio so that the user doesn't have to set tracespersecond to null.

[Copilot]

Pull request overview

This PR changes the default sampling behavior from 100% sampling (ApplicationInsightsSampler) to rate-limited sampling with 5.0 traces per second (RateLimitedSampler) to reduce telemetry costs for high-traffic applications. The change is implemented by setting the default value of TracesPerSecond property to 5.0 in both AzureMonitorExporterOptions and AzureMonitorOptions classes.

Key changes:

• Default sampler changed from 100% to rate-limited (5.0 traces/second) by setting TracesPerSecond = 5.0 as the default
• Configuration logic updated to automatically set TracesPerSecond = null when users explicitly configure only SamplingRatio via JSON configuration or environment variables
• All existing tests updated to reflect new defaults, and E2E tests explicitly configured for 100% sampling

Reviewed changes

Copilot reviewed 15 out of 15 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
sdk/monitor/Azure.Monitor.OpenTelemetry.Exporter/src/AzureMonitorExporterOptions.cs	Changed default value of TracesPerSecond from null to 5.0 and removed documentation stating 100% default
sdk/monitor/Azure.Monitor.OpenTelemetry.Exporter/src/DefaultAzureMonitorExporterOptions.cs	Added logic to set TracesPerSecond = null when only SamplingRatio is configured, enabling percentage-based sampling
sdk/monitor/Azure.Monitor.OpenTelemetry.AspNetCore/src/AzureMonitorOptions.cs	Changed default value of TracesPerSecond from null to 5.0 and removed documentation stating 100% default
sdk/monitor/Azure.Monitor.OpenTelemetry.AspNetCore/src/DefaultAzureMonitorOptions.cs	Added logic to set TracesPerSecond = null when only SamplingRatio is configured
sdk/monitor/Azure.Monitor.OpenTelemetry.Exporter/tests/Azure.Monitor.OpenTelemetry.Exporter.Tests/DefaultAzureMonitorExporterOptionsTests.cs	Updated tests to expect 5.0 as default and added new tests for configuration scenarios
sdk/monitor/Azure.Monitor.OpenTelemetry.AspNetCore/tests/Azure.Monitor.OpenTelemetry.AspNetCore.Tests/DefaultAzureMonitorOptionsTests.cs	Updated tests to expect 5.0 as default and added new test for TracesPerSecond configuration
sdk/monitor/Azure.Monitor.OpenTelemetry.AspNetCore/tests/Azure.Monitor.OpenTelemetry.AspNetCore.Tests/DefaultAzureMonitorOptionsSamplerTests.cs	Updated invalid argument tests to expect 5.0 as default
sdk/monitor/Azure.Monitor.OpenTelemetry.AspNetCore/tests/Azure.Monitor.OpenTelemetry.AspNetCore.Tests/InitializationTests.cs	Updated to expect rate-limited sampler as default
sdk/monitor/Azure.Monitor.OpenTelemetry.AspNetCore/tests/Azure.Monitor.OpenTelemetry.AspNetCore.Tests/E2ETests/*.cs	E2E tests configured to use 100% sampling for deterministic test results
sdk/monitor/Azure.Monitor.OpenTelemetry.Exporter/README.md	Added documentation for default sampling behavior and configuration examples
sdk/monitor/Azure.Monitor.OpenTelemetry.AspNetCore/README.md	Added documentation for default sampling behavior and configuration examples
sdk/monitor/Azure.Monitor.OpenTelemetry.Exporter/CHANGELOG.md	Documented breaking change with migration instructions
sdk/monitor/Azure.Monitor.OpenTelemetry.AspNetCore/CHANGELOG.md	Documented breaking change with migration instructions

[rajkumar-rangaraj]

LGTM