Add new Index advisor user doc

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[Oreoxmt]

/cc @qiancai

[qiancai]

Rest LGTM

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[LGTM Timeline notifier]

Timeline:

• 2025-03-17 02:39:30.772575743 +0000 UTC m=+236864.456811823: ☑️ agreed by qiancai.

[songrijie]

It seems we need include RECOMMEND INDEX in SQL reference, as it's a new syntax.

[songrijie]

Before actually adding the indexes, it's recommended to add invisible indexes, and verify the latency in session with tidb_opt_use_invisible_indexes=on. We shall mention this approach in this doc.

[qw4990]

It seems we need include RECOMMEND INDEX in SQL reference, as it's a new syntax.

I'll submit another PR to add this later.

[qw4990]

Before actually adding the indexes, it's recommended to add invisible indexes, and verify the latency in session with tidb_opt_use_invisible_indexes=on. We shall mention this approach in this doc.

This seems not work because invisible indexes also need to re-org data and cost lots of resources. You mean before removing an index, we can set it to invisible and check?