Add and use isSessionServerAllowed helper
What does this MR do?
fix this error when using helm and --set gitlab-runner.replicas=2
Error: template: empty/charts/gitlab-runner/templates/service-session-server.yaml:1:12: executing "empty/charts/gitlab-runner/templates/service-session-server.yaml" at <eq (default 1.0 .Values.replicas) 1.0>: error calling eq: incompatible types for comparison Use --debug flag to render out invalid YAML