syncer(dm): fix different output format for operate-schema get (#5824)

[ti-chi-bot]

This is an automated cherry-pick of #5824

What problem does this PR solve?

Issue Number: close #5688

What is changed and how it works?

• If the checkpoint doesn't exist and the schema is retrieved from the downstream, replace the downstream table name with the requested upstream table name

• Delete all \n in the SQL results for the operate-schema result

Check List

Tests

• Unit test

Questions

Will it cause performance regression or break compatibility? No.

Do you need to update user documentation, design documentation or monitoring documentation? No.

Release note

None

[ti-chi-bot]

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[ti-chi-bot]

@ti-chi-bot: This cherry pick PR is for a release branch and has not yet been approved by release team.
Adding the do-not-merge/cherry-pick-not-approved label.

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[lance6716]

no need to support v6.0