[TiDB] Add new mode option prefer-leader for tidb_replica_read.

[LykxSassinator]

Signed-off-by: Lucasliang [email protected]

First-time contributors' checklist

• I've signed Contributor License Agreement that's required for repo owners to accept my contribution.

What is changed, added or deleted? (Required)

Add a new mode prefer-leader for the system variable tidb_replica_read.

Which TiDB version(s) do your changes apply to? (Required)

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For details, see tips for choosing the affected versions (in Chinese).

• master (the latest development version)
• v6.6 (TiDB 6.6 versions)
• v6.5 (TiDB 6.5 versions)
• v6.4 (TiDB 6.4 versions)
• v6.1 (TiDB 6.1 versions)
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• v5.3 (TiDB 5.3 versions)
• v5.2 (TiDB 5.2 versions)
• v5.1 (TiDB 5.1 versions)
• v5.0 (TiDB 5.0 versions)

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

• This PR is translated from:
• Other reference link(s): [TiDB] Add a new mode prefer-leader for replica_read_mode. docs#12337

Do your changes match any of the following descriptions?

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

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• TomShawn

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[TomShawn]

LGTM

[LykxSassinator]

@TomShawn As all related PRs merged, this pr can be merged now.

[TomShawn]

This PR needs approval by @easonn7.

[easonn7]

LGTM

[TomShawn]

/remove-status LGT1
/status LGT2

[TomShawn]

/merge

[ti-chi-bot]

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

Commit hash: 78bd607