Cloud Gateways: Notifications in Notification Hub

## Jobs to be done (optional)
As a Kong Cloud Gateway user, I'd like more visibility and notifications for Data planes and Networks that are spinning up. Examples:
Additional management/visibility for various Dataplane states
Additional management/visibility for various Network states

With the launch of Notification Hub, DCGW should integrate errors and status using notification hub, and emails when events like DCGW dataplanes are ready for new deployments, notifications when gateways are updated, networks attached or when errors are present in the Gateways.

## Definition of done
- Document a new bulletpoint in https://developer.konghq.com/konnect-platform/notification-hub/ for DCGW and the notifications it supports

> [!IMPORTANT]
> This is a **Konnect release PR** and should be handed off to the PM to merge with the release once complete. Make sure you follow the [Konnect release checklist](https://github.com/Kong/developer.konghq.com/blob/main/docs/release-checklists.md#konnect-release-checklist).

## Information
Aha: https://konghq.aha.io/epics/KP-E-526

## Due date (optional)

March 2026 (deferred for managed cache v1.1 work)

## Size
Small

Start with the Notification Hub page linked in the issue and review the Konnect release checklist in docs/release-checklists.md. Add a bullet point documenting DCGW and the notifications it supports, then confirm the release handoff requirements are followed before considering the work done.

Written by the indexing model from the issue text.