docs: add upgrade guide for DefectDojo Pro on-premise (Helm) deployments (#15189)

Co-authored-by: Claude Fable 5 <noreply@anthropic.com>
Co-authored-by: Cody Maffucci <46459665+Maffooch@users.noreply.github.com>

Author: 3 people

docs/content/get_started/pro/onprem/upgrading.md

@@ -0,0 +1,31 @@
+---
+title: "Upgrading DefectDojo Pro (On-Premise)"
+description: "Supported upgrade procedure for self-hosted DefectDojo Pro deployments using the Helm chart"
+draft: false
+weight: 5
+audience: pro
+---
+
+This page describes the supported upgrade procedure for self-hosted DefectDojo Pro deployments that use the DefectDojo Pro Helm chart.
+
+## Upgrade everything as one unit
+
+Each DefectDojo Pro release consists of a Helm chart version, container image versions, and the Pro settings files. These are built and tested together and must be upgraded together as one unit.
+
+Upgrading only the image tags is not supported and will break your deployment.
+
+## Settings files and upgrades
+
+DefectDojo Pro ships a `pro_settings.py` file with every release, and the file changes with nearly every version. Do not carry a copy of `pro_settings.py` forward across upgrades, and do not patch an older copy by hand. The application must always run the `pro_settings.py` that matches its version.
+
+Put your own customizations in `local_settings.py`, never in `pro_settings.py`. Your `local_settings.py` is preserved across upgrades.
+
+The Helm chart ships and mounts the matching `pro_settings.py` and your `local_settings.py` automatically. When you upgrade using the chart, there is nothing to copy or migrate by hand.
+
+## Supported upgrade procedure
+
+1. Review the release notes for every version between your current version and your target version, not just the target itself. See the [DefectDojo Pro Changelog](/releases/pro/changelog/) and the version-specific [upgrade notes](/releases/os_upgrading/upgrading_guide/).
+2. Back up your database.
+3. Upgrade to the Helm chart release that matches your target application version, reusing your existing values files. Do not change image tags independently of the chart version.
+
+If you have questions about upgrading your on-premise deployment, contact [support@defectdojo.com](mailto:support@defectdojo.com).