Add missing Istio Operatorless templating function for Gitlab-runner

Description: The chart/templates/gitlab-runner/values.yaml is missing the IstioNamespaceSelector key and include function. This is required to pass down values the gitlab-runner package network policies.

Acceptance Criteria

• Add missing logic to the chart/templates/gitlab-runner/values.yaml
• Test that gitlab-runner network policies get the correct namespace selector labels applied