Draft: Schedule indexes for Ci backfill partition_id

What does this MR do and why?

This MR schedules async indexes which will be used by those migrations in order to speed them up as explained in our doc.

• Add partition_id to Ci::DailyBuildGroupReportRe... (!153236 - merged)
• Add partition_id to Ci::PipelineMessage (!153391 - merged)

See guideline at https://docs.gitlab.com/ee/development/database/adding_database_indexes.html#schedule-the-index-to-be-created

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