checkpoint(dm): check outdated should respect snapshot create time (#5160)

[ti-chi-bot]

This is an automated cherry-pick of #5160

Signed-off-by: lance6716 [email protected]

What problem does this PR solve?

Issue Number: close #5063

What is changed and how it works?

Old CheckGlobalPoint didn't check Snapshot creating time. Because we always use Snapshot to do a flush no matter it's a sync or async flush, we can always check that time

Check List

Tests

• Unit test

Code changes

• Has interface methods change

Side effects

Related changes

• Need to cherry-pick to the release branch

Release note

Fix a bug that checkpoint flushing will be called too frequently

[ti-chi-bot]

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[lance6716]

don't need fix bugs for v6.0