Use GOMAXPROCS instead of NumCPU

[eleboucher]

We can customize the number of CPU the application can use by setting gomaxprocs
therefore instead of using the max amount of cpu use the custom allowed max cpu count

[ggodik]

We don't have a voting system here but I vote against this change

1. This configuration should be explicitly set in applications - as it is currently passed into these functions. You can call StartConsuming("tag", runtime.GOMAXPROCS(0), ....) to achieve the same effect. This mechanism provides another path of configuration as a side effect - hence my downvote.
2. godocs say this function will go away when scheduling improves https://pkg.go.dev/runtime#GOMAXPROCS