[receiver/prometheusexec] Ensure factory test checks for the default intervals (#7594)
[receiver/prometheusexec] Ensure factory test checks for the default intervals (#7594)

* do not set scrape_timeout to fail test with 0 value

* use default values for wantPer

* add test to check zero value for default values

* remove test constants
open-telemetry/opentelemetry-collector-contrib,open-telemetry/opentelemetry-collector-contrib