Prepare async index creation for p_ci_pipelines trigger_id and id desc

What does this MR do and why?

To resolve the incident for https://gitlab.com/gitlab-com/request-for-help/-/issues/2518 and replace existing index p_ci_pipelines_trigger_id_idx, we will need to prepare async index creation for p_ci_pipelines trigger_id and id desc.

References

Screenshots or screen recordings

Before	After

How to set up and validate locally

MR acceptance checklist

Evaluate this MR against the MR acceptance checklist. It helps you analyze changes to reduce risks in quality, performance, reliability, security, and maintainability.

Related to #502767 (closed)