NGINX+ Support

[mpstefan]

As a potential user of NKG who has an NGINX+ subscription
I want NKG to have the ability to use NGINX+ for its data plane
So that I can leverage all of the NGINX+ features I enjoy with other NGINX products.

Background

Existing NGINX customers looking at using NGINX Kubernetes Gateway will also consider if they get any extra benefit for having an NGINX+ subscription. If not, we may end up taking sales away from NGINX; potentially threatening our own funding. There's a ton of additional value we can add instantly to NKG if we give the option of using NGINX+ as a data plane, including:

• Additional metrics
• Dynamic upstream reloads
• JWT Auth
• OIDC Support

We do need a method for users to be able to configure the above features, but we may be able to leverage what NGINX Ingress has already done to achieve this quickly.

Acceptance Criteria

• Users can choose to use NGINX+ instead of OSS NGINX through their configuration or during installation.
• Users can upgrade to NGINX+ if using OSS NGINX

For Discussion

• What steps are needed to optionally replace the data plane?
• How can we configure features provided by NGINX+?
  • Can we use Michael's NGINX configuration work to support these features?
  • Can we provide every feature immediately?
• Do we want to expose these features in configuration? When?

### Tasks
- [ ] https://github.com/nginxinc/nginx-gateway-fabric/issues/1329
- [ ] https://github.com/nginxinc/nginx-gateway-fabric/issues/1327
- [ ] https://github.com/nginxinc/nginx-gateway-fabric/issues/1330
- [ ] https://github.com/nginxinc/nginx-gateway-fabric/issues/1331
- [ ] https://github.com/nginxinc/nginx-gateway-fabric/issues/1332
- [ ] https://github.com/nginxinc/nginx-gateway-fabric/issues/1333
- [ ] https://github.com/nginxinc/nginx-gateway-fabric/issues/1334
- [ ] https://github.com/nginxinc/nginx-gateway-fabric/issues/1361
- [ ] https://github.com/nginxinc/nginx-gateway-fabric/issues/1381
- [ ] https://github.com/nginxinc/nginx-gateway-fabric/issues/1451
- [ ] https://github.com/nginxinc/k8s-dev/issues/43
- [ ] https://github.com/nginxinc/nginx-gateway-fabric/issues/1420