migration: Add information about non-MySQL to TiDB migration

[dveeden]

What is changed, added or deleted? (Required)

Add information about migrating from non-MySQL databases to TiDB.

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

• [x] master (the latest development version)
• [x] v5.1 (TiDB 5.1 versions)
• [x] 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)

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• morgo

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[dveeden]

https://docs.pingcap.com/tidb/stable/migration-tidb-faq#how-to-migrate-from-db2-or-oracle-to-tidb needs updating at some stage and/or link to this doc.

[qiancai]

Removed the needs-cherry-pick-release-6.4 label because the v6.4 docs have been archived at https://docs-archive.pingcap.com/tidb/v6.4 and will no longer receive new updates.

[qiancai]

Removed the needs-cherry-pick-release-6.6 label because the v6.6 docs have been archived at https://docs-archive.pingcap.com/tidb/v6.6 and will no longer receive new updates.

[ti-chi-bot[bot]]

PR needs rebase.

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[ti-chi-bot[bot]]

@dveeden: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-verify	9cc73dde3899cd51b22ee1834456c833dd3f83ef	link	true	/test pull-verify

Full PR test history. Your PR dashboard.

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