tidb: add the description for tidb_enable_auto_analyze_priority_queue

[Rustin170506]

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What is changed, added or deleted? (Required)

Added the description for the tidb_enable_auto_analyze_priority_queue variable.

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• [x] master (the latest development version)
• [x] v8.0 (TiDB 8.0 versions)
• [ ] v7.6 (TiDB 7.6 versions)
• [ ] v7.5 (TiDB 7.5 versions)
• [ ] v7.4 (TiDB 7.4 versions)
• [ ] v7.1 (TiDB 7.1 versions)
• [ ] v6.5 (TiDB 6.5 versions)
• [ ] v6.1 (TiDB 6.1 versions)
• [ ] v5.4 (TiDB 5.4 versions)
• [ ] v5.3 (TiDB 5.3 versions)
• [ ] v5.2 (TiDB 5.2 versions)
• [ ] v5.1 (TiDB 5.1 versions)
• [ ] v5.0 (TiDB 5.0 versions)

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• [ ] Delete files
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• [ ] Need modification after applied to another branch
• [ ] Might cause conflicts after applied to another branch

[ti-chi-bot[bot]]

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[LGTM Timeline notifier]

Timeline:

• 2024-03-14 07:48:07.69502653 +0000 UTC m=+930914.717272918: :ballot_box_with_check: agreed by Oreoxmt.
• 2024-03-18 01:39:27.720354781 +0000 UTC m=+1254394.742601164: :ballot_box_with_check: agreed by hfxsd.

[ti-chi-bot[bot]]

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[hfxsd]

/approve

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[APPROVALNOTIFIER] This PR is APPROVED

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