operate-schema: flush schema info and sync to master in optimistic mode (#1506)

[ti-srebot]

cherry-pick #1506 to release-2.0
You can switch your code base to this Pull Request by using git-extras:

# In dm repo:
git pr https://github.com/pingcap/dm/pull/1514

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

git push [email protected]:ti-srebot/dm.git pr/1514:release-2.0-976688affd66

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What problem does this PR solve?

handle rename column statement

What is changed and how it works?

• add --flush and --sync for operate-schema set
• flush checkpoint and table info
• sync table info to master and ignore conflict in optimistic mode

Check List

Tests

• Unit test
• Integration test

Code changes

• Has exported function/method change

[lance6716]

/lgtm