docs: Agent/add missing doc (#1207)

* docs: add config agent features

---------

Co-authored-by: Alan Dooley <[email protected]>

Author: JTorreG

content/nginx-one/agent/configure-instances/configure-agent-features.md

@@ -0,0 +1,100 @@
+---
+title: Review and configure features
+weight: 350
+toc: true
+nd-docs: DOCS-000
+nd-content-type: how-to
+---
+
+## Overview
+
+This guide describes the F5 NGINX Agent features, and how to enable and disable them using the NGINX Agent configuration file, CLI flags, environment variables, and gRPC updates.
+
+## Before you begin
+
+Before you start, make sure that you have:
+
+- [NGINX Agent installed]({{< ref "/nginx-one/agent/install-upgrade/" >}}) in your system.
+- Access to the NGINX Agent configuration file, CLI, or container environment.
+
+## Features
+
+The following table lists the NGINX Agent features:
+
+{{< table "features" >}}
+| Feature Name        | Description                                                                 | Default |
+| ------------------- | --------------------------------------------------------------------------- | ------- |
+| configuration       | Full read/write management of configurations, controlled by DataPlaneConfig ConfigMode. | On      |
+| certificates        | Inclusion of public keys and other certificates in the configurations toggled by DataPlaneConfig CertMode                 | Off     |
+| connection          | Sends an initial connection message reporting instance information on presence of Command ServerConfig Host and Port                 | On      |
+| file-watcher        | Monitoring of file changes in the allowed directories list and references from product configs.             | On      |
+| agent-api           | REST API for NGINX Agent.                                                    | Off     |
+| metrics             | Full metrics reporting.                                                      | On      |
+| > metrics-host      | Host-level metrics (cpu, disk, load, fs, memory, network, paging).           | On      |
+| > metrics-container | Container-level metrics from cgroup information.                             | On      |
+| > metrics-instance  | OSS and Plus metrics depending on NGINX instance.                            | On      |
+| logs                | Collection and reporting of NGINX error logs.                                | Off     |
+| > logs-nap          | F5 WAF for NGINX logs.                                                       | Off     |
+{{< /table >}}
+
+## Configuration sources
+
+You can enable or disable features using several configuration sources:
+
+### CLI parameters
+
+Enable features at launch:
+
+   ```shell
+   ./nginx-agent --features=connection,configuration,metrics,file-watcher,agent-api
+   ```
+
+### Environment variables
+
+Use environment variables for containerized deployments:
+
+   ```shell
+   export NGINX_AGENT_FEATURES="connection,configuration,metrics,file-watcher,agent-api"
+   ```
+
+### Configuration file
+
+Define features in the `nginx-agent.conf` file:
+
+   ```yaml
+   features:
+   - connection
+   - configuration
+   - metrics
+   - file-watcher
+   - agent-api
+   ```
+
+## Use cases
+
+### Enable metrics only
+
+1. Access the NGINX instance: Connect using SSH to the VM or server where NGINX Agent is running.
+
+   `ssh user@your-nginx-instance`
+
+1. Open the NGINX Agent configuration file in a text editor.
+
+   `sudo vim /etc/nginx-agent/nginx-agent.conf`
+
+1. Add the features section: Add the following to the end of the configuration file if it doesn't already exist.
+
+   ```yaml
+   features:
+   - metrics
+   - metrics-host
+   - metrics-container
+   - metrics-instance
+   ```
+
+1. Restart the NGINX Agent service to apply the changes.
+
+   `sudo systemctl restart nginx-agent`
+
+Once the steps have been completed, users will be able to view metrics data being sent but will not have the capability to push NGINX configuration changes.
+