Add timeout shutdown config to PeriodicMetricReader and its builder

[brunobat]

When using native instrumentation with the autoconfigure and custom executors we notice there is always a fixed 5s penalty on shutdown.
This causes unecessary delays on all tests instantiating metrics with a real PeriodicMeterReader and also ignores any timeout defined on the server side.

This PR exposes the value as a builder option while preserving the existing default.
The API change is just 2 new methods.

[otelbot]

⚠️ API changes detected — additional maintainer review required

@jack-berg @jkwatson

This PR modifies the public API surface area of the following module(s):

• opentelemetry-sdk-metrics

Please review the changes in docs/apidiffs/current_vs_latest/ carefully before approving.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 91.28%. Comparing base (e2efec5) to head (64f3e8b).
⚠️ Report is 1 commits behind head on main.

Additional details and impacted files

@@             Coverage Diff              @@
##               main    #8756      +/-   ##
============================================
- Coverage     91.29%   91.28%   -0.01%     
- Complexity    10498    10500       +2     
============================================
  Files          1006     1006              
  Lines         28338    28346       +8     
  Branches       3581     3582       +1     
============================================
+ Hits          25870    25877       +7     
  Misses         1675     1675              
- Partials        793      794       +1     

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Waiting on reviewers · refreshed 2026-09-02 14:35 UTC

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