* scraperhelper: use common scraping interface
This removes the MetricsScraper and ResourceMetricsScraper interfaces in favor
of a single Scraper interface that scrapes and returns pdata.Metrics. There
were already helper wrappers that allow users to return MetricSlices and
ResourceMetricSlices. These helpers package those results into pdata.Metrics
for the base interface.
Resolves#3085: This also removes the multiMetricScraper which wrapped multiple
scrapers to appear as a single scraper but then functions like scraper.ID()
would be empty. This was evident when trying to log errors and you couldn't
figure out what scraper made the error because it was wrapped in the
multiscraper.
* review updates
* Optimise the host metrics ticker logic by having one ticker per set of scrapers that use the same collection interval, and update tests
* Removed the ability to configure different collection intervals for different scrapers within the host metrics receiver & added documentation to note that the same effect can be achieved by configuring multiple receivers
* Change the Host Metrics scrapers from "ScrapeAndAppend" to "Scrape" and do the appending in the receiver instead
Jay Camp