Add ServerUrl helper

[maccabeelevine]

Abstract server URL generation away from the underlying Laminas view helper, as suggested by @demiankatz :

Maybe a good strategy would be to build a top-level service somewhere to get server URLs. The initial implementation could be a thin wrapper around the view helper, but that would result in a cleaner overall design, and might make it easier to swap out a different implementation in the future if we find ourselves needing to step back from the view helper approach.

And extracted from #4954 as also suggested

[demiankatz]

Thanks, @maccabeelevine!