[exporter/splunkhec] Surface and fix "no data" issue with Splunk HEC exporter, add test towards dropped records case

[atoulme]

Description:
Add a test showing what happens if we have a log record that is past what the collector can send.

Link to tracking Issue:
Fixes #20290

Testing:
Unit test

Documentation:
No changes

[runforesight]

Foresight Summary

    
Major Impacts

build-and-test-windows duration(3 seconds) has decreased 31 minutes 43 seconds compared to main branch avg(31 minutes 46 seconds).

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⭕  build-and-test-windows workflow has finished in 3 seconds (31 minutes 43 seconds less than main branch avg.) and finished at 3rd Apr, 2023.

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Job	Failed Steps	Tests
windows-unittest-matrix	-     🔗	N/A	See Details
windows-unittest	-     🔗	N/A	See Details

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✅  check-links workflow has finished in 54 seconds and finished at 3rd Apr, 2023.

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Job	Failed Steps	Tests
changed files	-     🔗	N/A	See Details
check-links	-     🔗	N/A	See Details

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✅  telemetrygen workflow has finished in 1 minute 15 seconds and finished at 3rd Apr, 2023.

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Job	Failed Steps	Tests
build-dev	-     🔗	N/A	See Details
publish-latest	-     🔗	N/A	See Details
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✅  build-and-test workflow has finished in 37 minutes 48 seconds (8 minutes 33 seconds less than main branch avg.) and finished at 3rd Apr, 2023.

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Job	Failed Steps	Tests
unittest-matrix (1.19, connector)	-     🔗	✅ 126  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.20, connector)	-     🔗	✅ 126  ❌ 0  ⏭ 0    🔗	See Details
correctness-metrics	-     🔗	✅ 2  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.19, internal)	-     🔗	✅ 583  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.20, internal)	-     🔗	✅ 583  ❌ 0  ⏭ 0    🔗	See Details
correctness-traces	-     🔗	✅ 17  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.20, extension)	-     🔗	✅ 544  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.19, extension)	-     🔗	✅ 544  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.19, processor)	-     🔗	✅ 1557  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.20, processor)	-     🔗	✅ 1557  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.19, receiver-0)	-     🔗	✅ 2616  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.20, receiver-0)	-     🔗	✅ 2616  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.19, exporter)	-     🔗	✅ 2510  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.20, receiver-1)	-     🔗	✅ 1965  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.20, exporter)	-     🔗	✅ 2510  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.19, receiver-1)	-     🔗	✅ 1965  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.20, other)	-     🔗	✅ 4761  ❌ 0  ⏭ 0    🔗	See Details
integration-tests	-     🔗	✅ 56  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.19, other)	-     🔗	✅ 4761  ❌ 0  ⏭ 0    🔗	See Details
setup-environment	-     🔗	N/A	See Details
check-collector-module-version	-     🔗	N/A	See Details
check-codeowners	-     🔗	N/A	See Details
checks	-     🔗	N/A	See Details
lint-matrix (receiver-0)	-     🔗	N/A	See Details
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build-examples	-     🔗	N/A	See Details
lint	-     🔗	N/A	See Details
unittest (1.20)	-     🔗	N/A	See Details
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cross-compile (linux, ppc64le)	-     🔗	N/A	See Details
cross-compile (linux, amd64)	-     🔗	N/A	See Details
cross-compile (windows, amd64)	-     🔗	N/A	See Details
build-package (deb)	-     🔗	N/A	See Details
build-package (rpm)	-     🔗	N/A	See Details
windows-msi	-     🔗	N/A	See Details
publish-check	-     🔗	N/A	See Details
publish-stable	-     🔗	N/A	See Details
publish-dev	-     🔗	N/A	See Details

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✅  changelog workflow has finished in 2 minutes 39 seconds and finished at 3rd Apr, 2023.

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Job	Failed Steps	Tests
changelog	-     🔗	N/A	See Details

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✅  prometheus-compliance-tests workflow has finished in 3 minutes 26 seconds (3 minutes less than main branch avg.) and finished at 3rd Apr, 2023.

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Job	Failed Steps	Tests
prometheus-compliance-tests	-     🔗	✅ 21  ❌ 0  ⏭ 0    🔗	See Details

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✅  load-tests workflow has finished in 7 minutes 10 seconds (3 minutes 18 seconds less than main branch avg.) and finished at 3rd Apr, 2023.

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Job	Failed Steps	Tests
loadtest (TestTraceAttributesProcessor)	-     🔗	✅ 3  ❌ 0  ⏭ 0    🔗	See Details
loadtest (TestIdleMode)	-     🔗	✅ 1  ❌ 0  ⏭ 0    🔗	See Details
loadtest (TestMetric10kDPS|TestMetricsFromFile)	-     🔗	✅ 6  ❌ 0  ⏭ 0    🔗	See Details
loadtest (TestTraceNoBackend10kSPS|TestTrace1kSPSWithAttrs)	-     🔗	✅ 8  ❌ 0  ⏭ 0    🔗	See Details
loadtest (TestTraceBallast1kSPSWithAttrs|TestTraceBallast1kSPSAddAttrs)	-     🔗	✅ 10  ❌ 0  ⏭ 0    🔗	See Details
loadtest (TestMetricResourceProcessor|TestTrace10kSPS)	-     🔗	✅ 12  ❌ 0  ⏭ 0    🔗	See Details
loadtest (TestBallastMemory|TestLog10kDPS)	-     🔗	✅ 18  ❌ 0  ⏭ 0    🔗	See Details
setup-environment	-     🔗	N/A	See Details

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✅  e2e-tests workflow has finished in 14 minutes 56 seconds and finished at 3rd Apr, 2023.

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Job	Failed Steps	Tests
kubernetes-test (v1.26.0)	-     🔗	N/A	See Details
kubernetes-test (v1.25.3)	-     🔗	N/A	See Details
kubernetes-test (v1.24.7)	-     🔗	N/A	See Details
kubernetes-test (v1.23.13)	-     🔗	N/A	See Details

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[dmitryax]

One nit, otherwise LGTM