Docs: High level data plane configuration overview

[sjberman]

As an NGF user,
I want to know what type of data plane fields I can configure,
So that I know how to change the settings of my data plane to fit my use case.

Acceptance

• A guide is created to give an overview of the NginxProxy CRD
• References to the API reference for NginxProxy, custom policy guide, and tracing policy guide are included in the data plane configuration guide.

Similar to how we have a control plane configuration page, it may be wise to include a high-level data plane configuration page. This doc could give a brief overview of things a user can configure, specifically using the NginxProxy resource, and then provide links to relevant docs that dive deeper, like the API reference, or tracing guide, or custom policies guide.

Chances are users will visit the Configuration section of our docs, looking for data plane information and not find it.