Update Upstreams with State Files for Dynamic Upstream Configuration

[mpstefan]

As a customer of NGINX Plus
I want NGF to dynamically update my upstreams when they change using state files
So that NGINX is not reloaded when it is not necessary through NGINX configuration via Agent.

Acceptance

Given NGF is using NGINX Plus as the data plane
When a configuration change is made where only the upstreams are changed
Then the state file is updated with proper Upstream values
And NGINX is not reloaded.

Dev Notes

• Does NOT need to be done in tandem with any Data and Control Plane Split epic work.
• When calling the N Plus API it will update the state file. NGF does not need to directly update the state file itself.

https://docs.nginx.com/nginx/admin-guide/load-balancer/dynamic-configuration-api/#configuring-persistence-of-dynamic-configuration