syncer: fix syncer gtid auto switch from off to on (#1723)

[ti-chi-bot]

This is an automated cherry-pick of #1723

What problem does this PR solve?

#1586 part 1

What is changed and how it works?

Add auto adjust gtid before we start a task.

Check List

Tests

• Unit test
• Integration test

Code changes

• Has exported function/method change
• Has exported variable/fields change

Side effects

• Possible performance regression
• Increased code complexity

Related changes

• Need to cherry-pick to the release branch
• Need to be included in the release note

[GMHDBJD]

LGTM

[ti-chi-bot]

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• GMHDBJD

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[lance6716]

waiting CI upgrading?

[lance6716]

dont know why master PR removed some lines in go.sum and passed CI, but this PR can't

[lance6716]

/merge

[ti-chi-bot]

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

Commit hash: 39c88b9