[mdatagen] Add ability to specify additional warnings in metadata.yaml

[dmitryax]

This is a follow-up change to #16536 adding the following warnings:

• if_enabled_not_set: to require enabled field to be explicitly set by users in case if the metric is going to be turned from optional to default and vice versa.

• if_configured: to ensure that users do not configure the metric. It should be used for deprecated optional metrics that will be removed soon.

This change also adds more test coverage for the metrics config unmarshaling

[runforesight]

Foresight Summary

    
Major Impacts

build-and-test duration(34 minutes 41 seconds) has decreased 25 minutes 16 seconds compared to main branch avg(59 minutes 57 seconds).

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⭕  build-and-test-windows workflow has finished in 3 seconds (43 minutes 36 seconds less than main branch avg.) and finished at 20th Dec, 2022.

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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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✅  tracegen workflow has finished in 1 minute 5 seconds (2 minutes 46 seconds less than main branch avg.) and finished at 20th Dec, 2022.

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build-dev	-     🔗	N/A	See Details
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✅  check-links workflow has finished in 1 minute 19 seconds (2 minutes 12 seconds less than main branch avg.) and finished at 20th Dec, 2022.

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changed files	-     🔗	N/A	See Details
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✅  changelog workflow has finished in 1 minute 41 seconds (7 minutes 21 seconds less than main branch avg.) and finished at 20th Dec, 2022.

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✅  prometheus-compliance-tests workflow has finished in 3 minutes 25 seconds (6 minutes 33 seconds less than main branch avg.) and finished at 20th Dec, 2022.

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

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✅  build-and-test workflow has finished in 34 minutes 41 seconds (25 minutes 16 seconds less than main branch avg.) and finished at 21st Dec, 2022.

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Job	Failed Steps	Tests
unittest-matrix (1.19, internal)	-     🔗	✅ 592  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.18, extension)	-     🔗	✅ 528  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.19, processor)	-     🔗	✅ 1474  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.18, internal)	-     🔗	✅ 592  ❌ 0  ⏭ 0    🔗	See Details
correctness-metrics	-     🔗	✅ 2  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.19, extension)	-     🔗	✅ 528  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.18, processor)	-     🔗	✅ 1474  ❌ 0  ⏭ 0    🔗	See Details
correctness-traces	-     🔗	✅ 17  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.18, receiver-0)	-     🔗	✅ 2539  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.19, receiver-0)	-     🔗	✅ 2539  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.19, exporter)	-     🔗	✅ 2456  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.18, exporter)	-     🔗	✅ 2456  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.18, other)	-     🔗	✅ 4394  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.18, receiver-1)	-     🔗	✅ 1871  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.19, receiver-1)	-     🔗	✅ 1871  ❌ 0  ⏭ 0    🔗	See Details
unittest-matrix (1.19, other)	-     🔗	✅ 4394  ❌ 0  ⏭ 0    🔗	See Details
integration-tests	-     🔗	✅ 55  ❌ 0  ⏭ 0    🔗	See Details
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build-package (rpm)	-     🔗	N/A	See Details
windows-msi	-     🔗	N/A	See Details
publish-check	-     🔗	N/A	See Details
publish-dev	-     🔗	N/A	See Details
publish-stable	-     🔗	N/A	See Details

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✅  load-tests workflow has finished in 8 minutes 30 seconds (8 minutes 59 seconds less than main branch avg.) and finished at 21st Dec, 2022.

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Job	Failed Steps	Tests
loadtest (TestIdleMode)	-     🔗	✅ 1  ❌ 0  ⏭ 0    🔗	See Details
loadtest (TestTraceAttributesProcessor)	-     🔗	✅ 3  ❌ 0  ⏭ 0    🔗	See Details
loadtest (TestTraceNoBackend10kSPS|TestTrace1kSPSWithAttrs)	-     🔗	✅ 8  ❌ 0  ⏭ 0    🔗	See Details
loadtest (TestTraceBallast1kSPSWithAttrs|TestTraceBallast1kSPSAddAttrs)	-     🔗	✅ 10  ❌ 0  ⏭ 0    🔗	See Details
loadtest (TestMetric10kDPS|TestMetricsFromFile)	-     🔗	✅ 6  ❌ 0  ⏭ 0    🔗	See Details
loadtest (TestMetricResourceProcessor|TestTrace10kSPS)	-     🔗	✅ 12  ❌ 0  ⏭ 0    🔗	See Details
loadtest (TestBallastMemory|TestLog10kDPS)	-     🔗	✅ 19  ❌ 0  ⏭ 0    🔗	See Details
setup-environment	-     🔗	N/A	See Details

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[dmitryax]

@astencel-sumo PTAL since you asked about it in #16536