docs(helm): document stable pod labels for Web Modeler anti-affinity rules

[bkenez]

Description

Document the existing pattern for upgrade-stable Web Modeler and Camunda Hub pod anti-affinity selectors across the Next, 8.9, 8.8, and 8.7 documentation.

The examples pair a user-owned Pod label with the same affinity selector, avoiding dependencies on Helm chart-managed labels. The guidance also covers namespace scope, topology labels, preferred versus required rules, and scheduler cost. The Next page now uses the current camundaHub.* values and links to the existing 8.9-to-8.10 migration guidance.

The guidance additionally states that the same podLabels and affinity pairing applies to every affinity-capable component, warns against selecting on chart-managed labels such as app.kubernetes.io/component, and notes that overriding the Orchestration Cluster (8.7: Zeebe) affinity replaces the default hard podAntiAffinity rule.

Related feature request: camunda/camunda-platform-helm#5876
Closes camunda/camunda-platform-helm#6932
Companion chart PR: camunda/camunda-platform-helm#6931

Local build and validation commands were not run; CI is the validation authority for this PR.

When should this change go live?

• This is a bug fix, security concern, or something that needs urgent release support. (add bug or support label)
• This is already available but undocumented and should be released within a week. (add available & undocumented label)
• This is on a specific schedule and the assignee will coordinate a release with the Documentation team. (create draft PR and/or add hold label)
• This is part of a scheduled alpha or minor. (add alpha or minor label)
• There is no urgency with this change (add low prio label)

PR Checklist

• The commit history of this PR is cleaned up, using {type}(scope): {description} commit message(s)

• My changes are for an upcoming minor release and are in the /docs directory.
• My changes are for an already released minor and are in a /versioned_docs directory.

• I added a DRI, team, or delegate as a reviewer for technical accuracy and grammar/style:
  • Engineering team review
  • Technical writer review via @camunda/tech-writers unless working with an embedded writer.

[giorgionaps]

LGTM!