add tests for internal metrics emitted via periodic metric reader

[codeboten]

As per @dmitryax's comment, there is insufficient unit test coverage of the telemetry emitted by the collector.

I'm worried that the emitted internal metrics are not covered by tests. It'll be great to see some metrics output changed in tests along with this change. @codeboten, do you know if we have a GH issue to introduce such coverage, by chance?

Originally posted by @dmitryax in #9775 (comment)

[nerudadhich]

Hi @codeboten, I would like to contribute on this. Would you be able to guide me with below findings ?

Should we add missing cases here in proctelemetry/config_test.go or we need to add more coverage for obsreport.go based on your PR results ?