Add index acceleration relatied sysvars and config var.

[Benjamin2037]

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[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• Oreoxmt
• tangenta

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All committers have signed the CLA.

[Oreoxmt]

@Benjamin2037 Could you please invite a tech review? Thanks

[Oreoxmt]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: ac97a21e99ca935124ab9dbdcf39b353b1459f92