[AzureMonitorExporter] Fix performance counters not using configured resource attributes (role name/instance)

[rajkumar-rangaraj]

Fixes #54618

Description

Fixed performance counter metrics not using configured cloud_RoleName and cloud_RoleInstance resource attributes (showing "unknown_service:appname" instead).

Root Cause

The internal MeterProvider created by StandardMetricsExtractionProcessor was initialized in the constructor before the processor was attached to the TracerProvider, so it couldn't access the configured resource attributes.

Solution

Changed MeterProvider to use lazy initialization with Lazy<T>. The lazy factory calls ParentProvider?.GetResource() to obtain resource attributes after the processor is attached to the TracerProvider, ensuring performance counters inherit the correct role name and instance.

Changes

• Modified StandardMetricsExtractionProcessor to use Lazy<MeterProvider?> for thread-safe lazy initialization
• Updated constructor signature to accept AzureMonitorMetricExporter parameter
• Updated call sites in ExporterRegistrationHostedService and AzureMonitorExporterExtensions
• Added test to verify performance counters use configured resource attributes

[Copilot]

Pull request overview

This PR fixes a bug where performance counter metrics were not using configured resource attributes (cloud_RoleName and cloud_RoleInstance), instead showing "unknown_service:appname". The root cause was that the internal MeterProvider was initialized in the constructor before the processor was attached to the TracerProvider, preventing access to configured resource attributes.

Key Changes:

• Changed MeterProvider initialization to use lazy initialization pattern to defer creation until after processor attachment
• Updated all test usages to access the lazy value via .Value property
• Added comprehensive test to verify the fix works correctly

Reviewed changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 3 comments.

File	Description
StandardMetricsExtractionProcessor.cs	Converted MeterProvider to Lazy<MeterProvider?> with deferred initialization that accesses ParentProvider.GetResource() to inherit resource attributes; removed unused import
StandardMetricTests.cs	Updated all existing tests to access _meterProvider.Value instead of _meterProvider directly; added new test to verify performance counters use configured resource attributes
CHANGELOG.md	Added entry documenting the bug fix (PR link placeholder needs completion)