Add new kb article for gitlab-kas redis error

Create a knowledge base article

💡 Please add any relevant links or information which inspired your knowledge base article, if applicable.

• Zendesk ticket: https://gitlab.zendesk.com/agent/tickets/584063
• GitLab issue link: gitlab-org/cluster-integration/gitlab-agent#669
• Slack discussion link:
• Any other relevant links:

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• Filename in format file_title_name.md
• Any example logs / commands have been generalized and customer information redacted
• Correct template used for article
• Empty headings are removed
• Related articles follow format: link description

Reviewers will publish once merged.