Add Enabled flag for attributes to metadata.yaml

[hughesjj]

Description: Adds an Enabled configuration option to metric generators so that receiver authors can add new attributes without forcing all existing consumers to use such.

Link to tracking Issue: 16373

Testing: make mdatagen-test && make generate
To verify I hit all of the resource_attributes in the various metadata.yaml, I installed yq and ran the below

rm resource_attr_metadata_yaml.log && grep -R --files-with-matches "resource_attributes" **/metadata.yaml | xargs yq .resource_attributes - >> resource_attr_metadata_yaml.log && echo "$(grep description resource_attr_metadata_yaml.log | wc -l) vs $(grep enabled resource_attr_metadata_yaml.log | wc -l)"
97 vs 97

I find it best to run something like this for new commits to this PR
make mdatagen-test && make generate && make otelcontribcol && git add -u && git commit -m "Meaningful update text" && git push

Documentation: None, other than changes to generated documentation.

[runforesight]

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build-and-test-windows duration(7 seconds) has decreased 41 minutes 13 seconds compared to main branch avg(41 minutes 20 seconds).

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⭕  build-and-test-windows workflow has finished in 7 seconds (41 minutes 13 seconds less than main branch avg.) and finished at 18th Jan, 2023.

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✅  tracegen workflow has finished in 1 minute 51 seconds and finished at 18th Jan, 2023.

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✅  build-and-test workflow has finished in 40 minutes 48 seconds (6 minutes 55 seconds less than main branch avg.) and finished at 18th Jan, 2023.

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✅  load-tests workflow has finished in 8 minutes 51 seconds (5 minutes 9 seconds less than main branch avg.) and finished at 18th Jan, 2023.

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Job	Failed Steps	Tests
loadtest (TestIdleMode)	-     🔗	✅ 1  ❌ 0  ⏭ 0    🔗	See Details
loadtest (TestTraceAttributesProcessor)	-     🔗	✅ 3  ❌ 0  ⏭ 0    🔗	See Details
loadtest (TestMetric10kDPS|TestMetricsFromFile)	-     🔗	✅ 6  ❌ 0  ⏭ 0    🔗	See Details
loadtest (TestTraceBallast1kSPSWithAttrs|TestTraceBallast1kSPSAddAttrs)	-     🔗	✅ 10  ❌ 0  ⏭ 0    🔗	See Details
loadtest (TestTraceNoBackend10kSPS|TestTrace1kSPSWithAttrs)	-     🔗	✅ 8  ❌ 0  ⏭ 0    🔗	See Details
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[dmitryax]

Few nits. Otherwise, LGTM. Please move if from draft once comments are addressed