sink(ticdc): make mysql sink support split transactions

[CharlesCheung96]

What problem does this PR solve?

Issue Number: close #5280

What is changed and how it works?

1. Add a SplitTxn field to RowChangedEvent, which identifies whether a transaction is split from the current event.
2. Split transactions in flow control module and record the size of transaction using txnSizeEntry.
3. Make sink support split transactions so that a single large transaction can be written concurrently to downstream, which can significantly reduce synchronization latency.

Note: In this PR, FlowControl system still release memory based on checkPointTs. After sink module supports batch resolve mechanism, FlowControl should release memory based on txnSizeEntry.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)

total row of txn: 2 million
txn size: ~360MB
downstream: tidb cluster

Code changes

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

Side effects

• Increased code complexity

Related changes

• Need to update the documentation
• Need to update key monitor metrics in both TiCDC document and official document

Release note

`Reduce mysql sink synchronization latency`.

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• amyangfei
• asddongmen

To complete the pull request process, please ask the reviewers in the list to review by filling /cc @reviewer in the comment.
After your PR has acquired the required number of LGTMs, you can assign this pull request to the committer in the list by filling /assign @committer in the comment to help you merge this pull request.

The full list of commands accepted by this bot can be found here.

Reviewer can indicate their review by submitting an approval review.
Reviewer can cancel approval by submitting a request changes review.

[CharlesCheung96]

/run-all-tests

[codecov-commenter]

Codecov Report

Merging #5281 (9ffb23c) into master (687e248) will decrease coverage by 0.1393%.
The diff coverage is 51.7150%.

Flag	Coverage Δ
cdc	61.0665% <51.7150%> (+0.4679%)	⬆️
dm	52.0276% <ø> (-0.4420%)	⬇️

Flags with carried forward coverage won't be shown. Click here to find out more.

@@               Coverage Diff                @@
##             master      #5281        +/-   ##
================================================
- Coverage   56.1240%   55.9846%   -0.1394%     
================================================
  Files           522        528         +6     
  Lines         65325      69519      +4194     
================================================
+ Hits          36663      38920      +2257     
- Misses        25094      26886      +1792     
- Partials       3568       3713       +145     

[CharlesCheung96]

/run-verify
/run-leak-test
/run-kafka-integration-test
/run-integration-test

[purelind]

/run-verify
/run-leak-test
/run-kafka-integration-test
/run-integration-test

[CharlesCheung96]

/run-all-tests

[CharlesCheung96]

/run-all-tests

[amyangfei]

/merge

[ti-chi-bot]

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

Commit hash: 8c28ec6