Change SpanExporter::export() return value to boolean

[Nevay]

Resolves #796.

[codecov]

Codecov Report

Merging #827 (812bf49) into main (b551294) will increase coverage by 0.00%.
The diff coverage is 97.43%.

Additional details and impacted files

@@            Coverage Diff            @@
##               main     #827   +/-   ##
=========================================
  Coverage     82.57%   82.57%           
- Complexity     1884     1885    +1     
=========================================
  Files           231      231           
  Lines          4901     4902    +1     
=========================================
+ Hits           4047     4048    +1     
  Misses          854      854           

Flag	Coverage Δ
7.4	82.58% <97.43%> (+<0.01%)	⬆️
8.0	82.61% <97.43%> (+<0.01%)	⬆️
8.1	82.61% <97.43%> (+<0.01%)	⬆️

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Impacted Files	Coverage Δ
src/Contrib/OtlpHttp/Exporter.php	83.67% <80.00%> (ø)
src/Contrib/Jaeger/AgentExporter.php	100.00% <100.00%> (ø)
src/Contrib/Jaeger/HttpCollectorExporter.php	58.33% <100.00%> (ø)
src/Contrib/Newrelic/Exporter.php	96.66% <100.00%> (ø)
src/Contrib/OtlpGrpc/Exporter.php	91.17% <100.00%> (ø)
src/Contrib/Zipkin/Exporter.php	100.00% <100.00%> (ø)
src/Contrib/ZipkinToNewrelic/Exporter.php	95.83% <100.00%> (ø)
.../SDK/Trace/Behavior/SpanExporterDecoratorTrait.php	100.00% <100.00%> (ø)
src/SDK/Trace/Behavior/SpanExporterTrait.php	100.00% <100.00%> (ø)
src/SDK/Trace/SpanExporter/ConsoleSpanExporter.php	100.00% <100.00%> (ø)
... and 3 more

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