Bump Redis version to 7.x for Cloud Provider Redis machines

What does this MR do?

Update elasticache_redis_engine_version and memorystore_redis_version versions to 7.x to align with GitLab's default version

Relevant docs - https://docs.gitlab.com/ee/install/requirements.html#redis

Related issues

Closes Bump Redis version to 7.x for Cloud Provider Re... (#710 - closed)

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.
  • 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.