Refactor Redis multi-node config to include defaults

What does this MR do?

It was discovered recently that the Redis docs were inaccurate for multi-node setups. As a result some components (Omnibus) weren't being configured to use Redis in these setups.

These components, Workhorse and KAS, currently expect the "default" Redis settings to be set alongside the separate queues. This may change in the future due to this finding but as it stands, and for previous versions, the defaults will be required. As such, MR shifts to this paradigm. Ironically we were already doing this in the charts by default as it's got a different config structure so this harmonizes Omnibus clients to follow the same approach.

Related issues

Closes #626 (closed)

Relates omnibus-gitlab#7419

Author's checklist

When ready for review, the Author applies the workflowready for review label and mention @gl-quality/get-maintainers:

• Merge request:
  • Corresponding Issue raised and reviewed by the GET maintainers team.
  • Merge Request Title and Description are up-to-date, accurate, and descriptive
  • MR targeting the appropriate branch
  • MR has a green pipeline
  • MR has no new security alerts in the widget from the Secret Detection and IaC Scan (SAST) jobs.
• Code:
  • Check the area changed works as expected. Consider testing it in different environment sizes (1k,3k,10k,etc.).
  • Documentation created/updated in the same MR.
  • If this MR adds an optional configuration - check that all permutations continue to work.
  • For Terraform changes: set up a previous version environment, then run a terraform plan with your new changes and ensure nothing will be destroyed. If anything will be destroyed and this can't be avoided please add a comment to the current MR.
• Create any follow-up issue(s) to support the new feature across other supported cloud providers or advanced configurations. Create 1 issue for each provider/configuration. Contact the Quality Enablement team if unsure.