[2.0.2] *: add transfer-source command (#605)

[ti-srebot]

cherry-pick #605 to release-2.0
You can switch your code base to this Pull Request by using git-extras:

# In docs-dm repo:
git pr https://github.com/pingcap/docs-dm/pull/617

After apply modifications, you can push your change to this PR via:

git push git@github.com:ti-srebot/docs-dm.git pr/617:release-2.0-e6b1139d79e2

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What is changed, added, or deleted? (Required)

align with pingcap/dm#1492

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

• master (the latest development version, including v3.0 changes)
• v2.0 (TiDB DM 2.0 versions)
• v1.0 (TiDB DM 1.0 versions)

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

• This PR is translated from:
• Other reference link(s):

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-srebot]

@lance6716 you're already a collaborator in bot's repo.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• CharLotteiu

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[lance6716]

/merge

[ti-chi-bot]

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

Commit hash: 6bd4478