feat: Add custom OTel configuration section

Author: aphralG

content/nginx-one/agent/metrics/configure-otel-metrics.md

@@ -39,3 +39,91 @@ You can validate that metrics are successfully exported by using the methods bel
       ```text
       Everything is ready. Begin running and processing data.
       ```
+
+### Custom OTel Configuration 
+
+NGINX Agent generates a default OpenTelemetry config to send metrics to your management plane located at `/etc/nginx-agent/opentelemetry-collector-agent.yaml`. An option is provided to 
+bring your own OpenTelemetry configs which will be merged with the NGINX Agent default config.
+
+OpenTelemetry will merge your [OpenTelemetry Config](https://opentelemetry.io/). The order of the OpenTelemetry config files matters, 
+the last config in the list will take priority over others listed if they have the same value configured.
+
+To have NGINX Agent use your own OpenTelemetry config:
+
+1. Edit the configuration file `sudo vim /etc/nginx-agent/nginx-agent.conf`
+2. Add the collector property
+
+```yaml
+collector:
+  additional_config_paths:
+    - "/my_config.yaml"
+```
+
+### Example usage: 
+
+{{< call-out "important" >}} NGINX Agent uses `/default` for naming its default processors, exporters and pipelines using the same naming in your own config might cause issues with sending metrics to your management plane {{< /call-out >}}
+
+#### Add Prometheus Exporter
+```yaml
+exporters:
+  prometheus:
+    endpoint: "127.0.0.1:5643"
+    resource_to_telemetry_conversion:
+      enabled: true
+
+service:
+  pipelines:
+    metrics/prometheus-example-pipeline:
+      receivers:
+        - containermetrics
+        - hostmetrics
+      processors:
+        - resource/default
+      exporters:
+        - prometheus
+```
+
+#### Add Debug Exporter
+```yaml
+exporters:
+  debug:
+    verbosity: detailed
+    sampling_initial: 5
+    sampling_thereafter: 200
+
+service:
+  pipelines:
+    metrics/debug-example-pipeline:
+      receivers:
+        - containermetrics
+        - hostmetrics
+      processors:
+        - resource/default
+      exporters:
+        - debug
+```
+
+
+#### Debug Merging Configs
+
+To view the merged OpenTelemetry configuration set the Agent log level to debug in `/etc/nginx-agent/nginx-agent.conf` and restart NGINX Agent 
+
+1. Edit the configuration file `sudo vim /etc/nginx-agent/nginx-agent.conf`
+2. Change the log property
+```yaml
+log:
+  level: debug 
+```
+3. Restart NGINX Agent 
+4. View merged OpenTelemetry configuration `cat /var/lib/nginx-agent/opentelemetry-collector-agent-debug.yaml`
+
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