Add introduction of how to migrate Aurora to TiDB with DM

[sunzhaoyang]

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• [x] master (the latest development version)
• [x] v6.1 (TiDB 6.1 versions)
• [x] v6.0 (TiDB 6.0 versions)
• [x] 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)
• [ ] v4.0 (TiDB 4.0 versions)
• [ ] v3.1 (TiDB 3.1 versions)
• [ ] v3.0 (TiDB 3.0 versions)
• [ ] v2.1 (TiDB 2.1 versions)

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[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• ran-huang

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[sunzhaoyang]

/cc @ran-huang @lance6716

[ran-huang]

@sunzhaoyang Check out 51fe819. The rest LGTM!

[ran-huang]

@lance6716 PTAL

[ti-chi-bot]

@sunzhaoyang: PR needs rebase.

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[qiancai]

Removed the needs-cherry-pick-release-6.6 label because the v6.6 docs have been archived at https://docs-archive.pingcap.com/zh/tidb/v6.6 and will no longer receive new updates.

[qiancai]

Removed the needs-cherry-pick-release-7.0 label because the v7.0 docs have been archived at https://docs-archive.pingcap.com/zh/tidb/v7.0 and will no longer receive new updates.

[qiancai]

Removed the needs-cherry-pick-release-7.2 label because the v7.2 docs have been archived at https://docs-archive.pingcap.com/zh/tidb/v7.2 and will no longer receive new updates.