feat: Enable automatic DB reindexing in CNG installations

What does this MR do?

feat: Enable automatic DB reindexing in CNG installations

Related to gitlab-com/gl-infra/delivery#21668

Automatic database reindexing is possible in Omnibus installation by flipping some configuration values inside the gitlab.rb file. As far as I can tell, Helm chart installations that use CNG (Cloud Native GitLab) container images do not have a native method for runnig reindexing periodically.

The Toolbox chart already has a CronJob for taking a backup. So, I am proposing that we add a CronJob that will perform automatic database reindexing on a user-specified schedule: gitlab-org/charts/gitlab!4665

Related issues

Checklist

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• Merge Request Title, and Description are up to date, accurate, and descriptive
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Expected (please provide an explanation if not completing)

• Test plan indicating conditions for success has been posted and passes
• Documentation created/updated
• Integration tests added to GitLab QA
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