add doc for tikv-client.enable-replica-selector-v2

[crazycs520]

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What is changed, added or deleted? (Required)

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What is the related PR or file link(s)?

• Other reference link(s): enable replica-selector-v2 by default tikv/client-go#1229

Do your changes match any of the following descriptions?

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

[lilin90]

/lgtm

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2024-03-20 06:22:57.457492823 +0000 UTC m=+1444204.479739203: ☑️ agreed by qiancai.
• 2024-03-21 09:27:02.292595079 +0000 UTC m=+1541649.314841467: ☑️ agreed by lilin90.

[qiancai]

/approve

[ti-chi-bot]

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