go_library to have a pure attribute

When a library depends on another library that requires CGO, there is no way for that library to be declared as "pure=off"

The only alternative are to define our own rule with a transition or to mark that go_library as manual to not be trapped by wildcards.

Our bazelrc defaults to pure=on which applies this to every target and we need to declare pure=off on the go_binary but it would be better if the pure=off was set on the go_library that needs to be impure directly

Start at the go_library rule entry point and review how pure is currently handled, using the bazelrc default described in the issue as context. Determine how an impure dependency should be declared directly on a go_library, then verify that the setting is respected when the target is selected through wildcards and built through a dependent go_binary.

Written by the indexing model from the issue text.