Separate control plane and data plane

[kate-osborn]

Parent issue: #292

Separate the control plane and data plane by deploying them in separate Pods. Update the deployment manifests so the user can deploy the control and data planes separately. More information here: https://github.com/nginxinc/nginx-kubernetes-gateway/blob/main/design/control-data-plane-separation/design.md#deployment-architecture.

Consider the following when writing the data plane manifests:

• static configuration files should be mounted to the Pod
• liveness/readiness probes may target different processes

A/C:

• Control and data planes are installed separately via manifests
• Data plane can be installed as a Deployment
• Both control plane and data planes should run with least privileges
• Installation docs are updated to reflect new process

Aha! Link: https://nginx.aha.io/features/NKG-33

[pleshakov]

Data plane can be installed as a DaemonSet or Deployment

let's reduce to just deployment for now? I think once we introduce Helm (or/and some other tool) we can expand installation options