sink/mysql: support translated to insert SQL if old value enabled

[amyangfei]

What problem does this PR solve?

In MySQL sink, insert is translated to REPLACE SQL, update is translated to DELETE + REPLACE SQL

When old value feature is enabled, we can distinguish whether a SQL is update or insert, so we can translate insert to INSERT SQL and update to UPDATE SQL to increase executing performance.

But in some cases, update and insert is not reentrant, we also need the safe-mode mechanism to force write data.

Besides, the more convenient safe-mode switch will be implemented in another PR.

What is changed and how it works?

• Introduce a new safe-mode option in MySQL sink
• The SQL translator behavior, when the old value feature is enabled, is as follows

	insert	update
in safe mode	REPLACE	DELETE + REPLACE
not in safe mode	INSERT	UPDATE

Check List

Tests

• Unit test
• Integration test

Release note

• Support to translate to more execution efficient SQLs in MySQL sink when the old value feature is enabled.

[amyangfei]

/run-integration-tests tidb=release-4.0 tikv=release-4.0 pd=release-4.0

[amyangfei]

/run-integration-tests tidb=release-4.0 tikv=release-4.0 pd=release-4.0

[overvenus]

LGTM

[amyangfei]

/run-integration-tests tidb=release-4.0 tikv=release-4.0 pd=release-4.0

[liuzix]

/lgtm

[amyangfei]

/run-integration-tests tidb=release-4.0 tikv=release-4.0 pd=release-4.0

[codecov-commenter]

Codecov Report

Merging #955 into master will increase coverage by 0.0315%.
The diff coverage is 35.4545%.

@@               Coverage Diff                @@
##             master       #955        +/-   ##
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+ Coverage   33.5889%   33.6204%   +0.0315%     
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  Files           100        100                
  Lines         11998      12073        +75     
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+ Hits           4030       4059        +29     
- Misses         7573       7615        +42     
- Partials        395        399         +4