Add Prometheus imagePullSecrets configuration for air-gapped installations

Author: gshaibi

docs/admin/runai-setup/cluster-setup/cluster-prerequisites.md

@@ -227,6 +227,7 @@ helm install prometheus prometheus-community/kube-prometheus-stack \
 1. The Grafana component is not required for Run:ai.
 
 !!! Notes
+    * In an air-gapped environment, if needed, configure the `global.imageRegistry` value to reference the local registry hosting the Prometheus images.
     * For troubleshooting information, see the [Prometheus Troubleshooting Guide](https://github.com/prometheus-operator/prometheus-operator/blob/main/Documentation/troubleshooting.md){target=_blank}.
 
 ## Optional Software Requirements

docs/admin/runai-setup/cluster-setup/customize-cluster-install.md

@@ -40,6 +40,7 @@ All customizations will be saved when upgrading the cluster to a future version.
 | `global.nodeAffinity.restrictScheduling` | false | Restrict scheduling of workloads to specific nodes, based on node labels. For more information see [node roles](../config/node-roles.md#dedicated-gpu--cpu-nodes) |
 | `spec.prometheus.spec.retention` | 2h | The interval of time where Prometheus will save Run:ai metrics. Promethues is only used as an intermediary to another metrics storage facility and metrics are typically moved within tens of seconds, so changing this setting is mostly for debugging purposes. |
 | `spec.prometheus.spec.retentionSize` | Not set | The amount of storage allocated for metrics by Prometheus. For more information see [Prometheus Storage](https://prometheus.io/docs/prometheus/latest/storage/#operational-aspects){target=_blank}. |
+| `spec.prometheus.spec.imagePullSecrets` | Not set | An optional list of references to secrets in the runai namespace to use for pulling Prometheus images (relevant for air-gapped installations). |
 
 ## Understanding Custom Access Roles