feat: Update cluster defaults package with network policies

[borkodjurkovic-ssc]

Summary

In order to comply with the nist-sp-800-53-r5-require-namespace-network-policies constraint (of NIST SP 800-53 Rev. 5 Policy Controller bundle), cluster-defaults package required updates to add network policies to the gateway-infra and default namespaces.

gateway-infra namespace Network Policy

Added cluster-defaults/admin-namespaces/networkpolicy.yaml file to implement network policy in the gateway-infra namespace.

Network policies implement following rules:

• Allow ingress within namespace
• Allow ingress from lb health check
• Allow egress within namespace
• Allow egress to metadata server
• Allow egress for GCP API
• Allow egress to private IP ranges (includes K8S cluster)

default namespace Network Policy

Added cluster-defaults/default-namespace/networkpolicy.yaml file to implement network policy in the default namespace

Network policies implement following rules:

• Allow ingress within namespace
• Allow egress within namespace

[fmichaelobrien]

Lgtm

[fmichaelobrien]

Doing a deeper review around general 800-53 later tonight

[alaincormier-ssc]

added a few minor comments

[fmichaelobrien]

/lgtm