Add sync creation of next_over_limit_check_at index

What does this MR do and why?

This is step two of the index creation for index_next_over_limit_check_at_asc_order.

As stated in the docs, this should result on a no-op on Gitlab.com since the actual index has already been created in a post-deployment migration (see screenshot).

Refs:

• Create the `index_next_over_limit_check_at_asc_... (#391830 - closed) • SAM FIGUEROA • 15.10
• Add index for next_over_limit_check_at (!111819 - merged) • SAM FIGUEROA • 15.9
• Follow-up from "Add workers to notify over limi... (#391296 - closed) • SAM FIGUEROA
• Add workers to notify over limit owners (!98438 - merged) • SAM FIGUEROA • 15.9
• https://gitlab.com/gitlab-org/gitlab/-/issues/367549+s

Screenshots or screen recordings

How to set up and validate locally

1. rails db:migrate

MR acceptance checklist

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