Prototype for NGINX Agent Connection and Registration

[mpstefan]

As a maintainer of NGF
I want to do an early prototype of NGF integrating with the connection and registration feature of NGINX Agent
So that I can give the Agent team feedback for integration in preparation for data and control plane separation.

Acceptance

• An NGF environment is created that integrates with NGINX Agent's connection and registration feature.
• Feedback on Agent integration is relayed to the NGINX Agent team.

[sjberman]

Initial PoC here: https://github.com/sjberman/nginx-gateway-fabric/tree/poc/agent-connection