Add IP masquerade agent

This installs IP masquerad agent in the cluster during its creation. By specifying nonMasqueradeCIDRs in the configMap, GKE preserves the source IPs as pod IPs for packets sent to destinations specified in nonMasqueradeCIDR.

A typical scenario is connecting cluster to services running in on-prem network.

No longer needed for https://gitlab.developers.cam.ac.uk/uis/moodle/moodle-cloud/deployment/-/issues/21

Part of (but doesn't close) https://gitlab.developers.cam.ac.uk/uis/moodle/moodle-cloud/deployment/-/issues/61