Remove old global meter provider shutdown method

[jtescher]

Changes

This change removes the old global::shutdown_meter_provider method which is not part of the metrics API spec, and properly documents the SdkMeterProvider::shutdown method which is spec compliant.

Merge requirement checklist

• CONTRIBUTING guidelines followed
• Unit tests added/updated (if applicable)
• Appropriate CHANGELOG.md files updated for non-trivial, user-facing changes
• Changes in public API reviewed (if applicable)

[codecov]

Codecov Report

Attention: 2 lines in your changes are missing coverage. Please review.

Comparison is base (897e70a) 57.3% compared to head (4e5d723) 57.3%.
Report is 1 commits behind head on main.

Files	Patch %	Lines
opentelemetry-sdk/src/attributes/set.rs	88.8%	2 Missing ⚠️

Additional details and impacted files

@@          Coverage Diff          @@
##            main   #1412   +/-   ##
=====================================
  Coverage   57.3%   57.3%           
=====================================
  Files        146     146           
  Lines      18179   18184    +5     
=====================================
+ Hits       10422   10434   +12     
+ Misses      7757    7750    -7     

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[Oliboy50]

ℹ️ I opened a discussion here to find a valid replacement for when the MeterProvider is not easily accessible, since the removal of global::shutdown_meter_provider.

[lalitb]

@Oliboy50 This issue is specific to the MetricsLayer provided by tracing-opentelemetry. And not while using the Otel Metrics API from this repo. Would you like to open a discussion within that repo. As I replied in our discussion:

I think your workaround should work (though good to validate it), but the solution should be for the MetricsLayer layer to take either instance of Meter, or the non-mutable reference to MeterProvider as an argument, as done for traces and logs. This will allow the MeterProvider instance to be used by the application for shutdown and flush calls.

[Oliboy50]

@lalitb Following your advices, I opened a discussion there