Backport Redis migration to 16.8

What does this MR do and why?

Backport of !141809 (merged) to 16.8.

This migration should have been part of 16.8 but was removed in !140587 (merged) due to a bug.

The code change was released in 16.8 without the migration, which means that the metrics redis_hll_counters.code_review.i_code_review_create_mr_monthly and redis_hll_counters.code_review.i_code_review_create_mr_weekly will be wrong for the first month after an instance i upgraded to 16.8.

By getting the migration out as soon as possible we will prevent this data-loss happening for a large amount of instances.

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

• This MR is backporting a bug fix, documentation update, or spec fix, previously merged in the default branch.
• The MR that fixed the bug on the default branch has been deployed to GitLab.com (not applicable for documentation or spec changes).
• This MR has a severity label assigned (if applicable).
• Set the milestone of the merge request to match the target backport branch version.
• This MR has been approved by a maintainer (only one approval is required).
• Ensure the e2e:package-and-test-ee job has either succeeded or been approved by a Software Engineer in Test.

Note to the merge request author and maintainer

If you have questions about the patch release process, please:

• Refer to the patch release runbook for engineers and maintainers for guidance.
• Ask questions on the #releases Slack channel (internal only).