refactor scraper in azuremonitorreceiver

[nslaughter]

Component(s)

receiver/azuremonitor

Describe the issue you're reporting

The azuremonitorreceiver scraper needs refactoring to clarify code, which will allow us to address bugs with zero-values sometimes as reported in #34265.

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[crobert-1]

Issue was filed by a code owner and makes sense to me, removing needs triage.