expanded exporter APIs with explicitTimeout on force flush and shutdown

[bryce-b]

This fixes the issue where a processor is called with an explicit timeout, but the timeout isn't propogated to the exporter as it should be.

[bryce-b]

This PR fixed #449 and #457/#455

[codecov]

Codecov Report

Patch coverage is 79.02% of modified lines.

❗ Current head e07717e differs from pull request most recent head cbaad29. Consider uploading reports for the commit cbaad29 to get more accurate results

Files Changed	Coverage
Sources/Exporters/Jaeger/JaegerSpanExporter.swift	0.00%
.../Persistence/PersistenceLogExporterDecorator.swift	0.00%
...lemetrySdk/Logs/Export/NoopLogRecordExporter.swift	0.00%
...rySdk/Logs/Processors/NoopLogRecordProcessor.swift	0.00%
...Sdk/Logs/Processors/SimpleLogRecordProcessor.swift	0.00%
Sources/Exporters/Zipkin/ZipkinTraceExporter.swift	20.00%
...enTelemetrySdk/Logs/Export/LogRecordExporter.swift	33.33%
...emetrySdk/Logs/Export/MultiLogRecordExporter.swift	47.36%
...emetrySdk/Logs/Processors/LogRecordProcessor.swift	50.00%
...etryProtocolHttp/trace/OtlpHttpTraceExporter.swift	53.70%
... and 22 more

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