Metricbeat module with multiple metricsets overwrites the error status set by a previous metricset

[mauri870]

While investigating elastic/elastic-agent#6155, @VihasMakwana pointed out that if a Metricbeat module contains multiple metricsets, an error reported by one metricset is overwritten by another. This was tested with the latest DRA (8.17.0) of Elastic Agent.

The scenario goes like this:

1. One metricset Fetch call reports a partial metrics error
2. Almost immediately a new metricset from the same module reports a success
3. The status of the previous metricset gets overwritten and it reports the status as success.
4. Go to step 1, loop and repeat forever. Due to how fast this happens, the error is never shown to the user.

Here it says that PartialMetricsError is temporary and will be removed at some point, but we started using it in more than one place. I propose we remove this comment.

The likely cause of this issue appears to be in the following code that is called for the error result of a metricset Fetch op: metricbeat/mb/module/wrapper.go#L313-L336.

[elasticmachine]

Pinging @elastic/elastic-agent-data-plane (Team:Elastic-Agent-Data-Plane)