Allow overwriting the terminationGracePeriodSeconds value for runner manager pod

For helm chart installations, it is possible to change the default terminationGracePeriodSeconds value for runner manager pod.

Unfortunately, there is no way to change it for installations with OpenShift operator: available operator properties.

Customer ticket where we discussed terminationGracePeriodSeconds: https://gitlab.zendesk.com/agent/tickets/329544 (link is internal)