Add SDK TracerProviderInterface to expose ::shutdown() and ::forceFlush()

[Nevay]

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[codecov]

Codecov Report

Merging #756 (2d95cc5) into main (8e30ea0) will not change coverage.
The diff coverage is 100.00%.

@@            Coverage Diff            @@
##               main     #756   +/-   ##
=========================================
  Coverage     82.86%   82.86%           
  Complexity     1295     1295           
=========================================
  Files           150      150           
  Lines          3192     3192           
=========================================
  Hits           2645     2645           
  Misses          547      547           

Flag	Coverage Δ
7.4	82.87% <100.00%> (ø)
8.0	82.92% <100.00%> (ø)
8.1	82.92% <100.00%> (ø)

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Impacted Files	Coverage Δ
src/SDK/Trace/TracerProvider.php	65.00% <100.00%> (ø)
src/SDK/Trace/TracerProviderFactory.php	100.00% <100.00%> (ø)

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