Update eks cluster config to not imply multi-region

[conceptualshark]

Description

Resolves #4259 - the EKS page has a code block which references # Multi-region zones which is misleading, as it is just referring to multiple zones for the region (not multiple regions). This PR removes "region" from the comment.

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 DevEx 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

• My changes are for an upcoming minor release and:
  • are in the /docs directory (version 8.8).
  • are in the /versioned_docs/version-8.7/ directory (version 8.7).
• 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.