*: add docs for TiFlash MinTSO scheduler (#18621)

[ti-chi-bot]

This is an automated cherry-pick of #18621

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• v8.3 (TiDB 8.3 versions)
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What is the related PR or file link(s)?

• This PR is translated from:
• Other reference link(s): Add tiflash mintso doc #18542

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• Delete files
• Change aliases
• Need modification after applied to another branch
• Might cause conflicts after applied to another branch

[lilin90]

/approve

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