[receiver/dockerstats] Disable container.cpu.usage.system by default, and expand description

[jamesmoessis]

Description:

• container.cpu.usage.system is no longer a default metric.
• Added more description for the metric, since I believe it had the possibility to mislead users.

My rationale behind disabling this as a default metric, is that it has the potential to be misleading unless the user has explicitly read the description. It also duplicates system CPU metrics emitted by the hostmetricsreceiver. I thought about completely removing it, but I thought I better leave it in since it is something that docker reports.

Change is technically breaking, but only behind the non-default featuregate. I don't expect it will impact any users.

Link to tracking Issue: #9794

Testing:

Tests were updated to test for the updated description

Documentation:

Go generate / mdatagen updates the docs.

[jamesmoessis]

FYI @MovieStoreGuy @rmfitzpatrick

[bogdandrutu]

@open-telemetry/collector-contrib-approvers how do you want to do this?

[MovieStoreGuy]

@bogdandrutu , not an approver but as I understand that this change is a low risk due to the fact that receiver has yet to adopt the version 2 of the scraper as the default. (Version 2 captures metrics using the generated metrics file)

[mx-psi]

IMHO since the stability of this feature gate is alpha

opentelemetry-collector-contrib/receiver/dockerstatsreceiver/factory.go

Line 40 in f9e2bcb

Enabled: false,

we just need to list the change as breaking and move on. The whole point of feature gates is to allow doing breaking changes more quickly, we should make clear that this is breaking but that's about it.

[dmitryax]

If it's behind a feature gate that is disabled by default, I believe we can move on