Puts 'global.kas.apiExternalPort' in top-level values.yaml because
globals should "flow downstream" - meaning the globals should be set
in the parent chart for consumption by child/sibling charts.

Helm 3.7.0 includes a change that enforces this approach, meaning that
enabling KAS in the GitLab Charts would cause a failure because the
Webservice ConfigMap could not find the `global.kas.apiExternalPort`
value (because it was in the KAS chart, its sibling).

Reference issue in Helm project:
https://github.com/helm/helm/issues/10154#issuecomment-923120990

Changelog: fixed