Fix hostmetricsreceiver/processscraper tests to work for darwin

[8naama]

Description:

• Excluded darwin unsupported metrics from testCases, 'metricsLen', default config
• Excluded from testCases the 'Parent PID Error' test since it's excluded in the code
• Added darwin specific test case for Cmdline()

Not sure I took the best approach here (as I also added a function to a DO NOT EDIT file - generated_metrics.go), will love your feedback!

Link to tracking Issue: Issue #19141

Testing:
Tested locally on Mac to make sure metrics are collected and that running go test at the ./hostmetricsreceiver/internal/scraper/processscraper folder for returns PASS

Documentation:
added notes for excluding unsupported metrics

[runforesight]

Foresight Summary

    
Major Impacts

build-and-test-windows duration(6 seconds) has decreased 31 minutes 13 seconds compared to main branch avg(31 minutes 19 seconds).

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⭕  build-and-test-windows workflow has finished in 6 seconds (31 minutes 28 seconds less than main branch avg.) and finished at 8th Apr, 2023.

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Job	Failed Steps	Tests
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✅  check-links workflow has finished in 44 seconds and finished at 8th Apr, 2023.

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✅  telemetrygen workflow has finished in 1 minute 3 seconds and finished at 8th Apr, 2023.

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✅  prometheus-compliance-tests workflow has finished in 3 minutes 20 seconds (2 minutes 55 seconds less than main branch avg.) and finished at 8th Apr, 2023.

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✅  load-tests workflow has finished in 6 minutes 18 seconds (4 minutes 4 seconds less than main branch avg.) and finished at 8th Apr, 2023.

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loadtest (TestTraceNoBackend10kSPS|TestTrace1kSPSWithAttrs)	-     🔗	N/A	See Details
loadtest (TestTraceBallast1kSPSWithAttrs|TestTraceBallast1kSPSAddAttrs)	-     🔗	N/A	See Details
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✅  e2e-tests workflow has finished in 10 minutes 56 seconds (3 minutes 10 seconds less than main branch avg.) and finished at 8th Apr, 2023.

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✅  build-and-test workflow has finished in 23 minutes 58 seconds (22 minutes 37 seconds less than main branch avg.) and finished at 9th Apr, 2023.

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Job	Failed Steps	Tests
lint-matrix (other)	-     🔗	N/A	See Details
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cross-compile (darwin, amd64)	-     🔗	N/A	See Details
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[andrzej-stencel]

@8naama, the tests in process_scraper_test.go are still being skipped on MacOS, as described in the issue:

the skipTestOnUnsupportedOS helper disables tests for metrics that are now supported on Darwin.

These tests need to be run on MacOS as well as on Linux and Windows.

[8naama]

Thank you @astencel-sumo !! Sorry, I probably had a mistake when working on it and accidentally removed the line when I enabled it and my tests last commit were wrong. 🤦🏻‍♀️

I made sure it's enabled now and re-tested everything

[andrzej-stencel]

Thanks @8naama, this fixes the tests (just fix the "deafult" typos that the bot has diligently pointed out ;)).

I'm worried that this change introduces even more complexity into this already too complicated test code. Ideally, these tests should be refactored for better maintainability, to have less "if" conditions all over the place. I think this is a task for another PR though.

What do you think @dmitryax?

[dmitryax]

I agree. It would be great to simplify the test code overall, but not required for this PR