sinkv2(ticdc): impl TxnEventAppender and add tests

[Rustin170506]

What problem does this PR solve?

Issue Number: ref #5928

What is changed and how it works?

impl TxnEventAppender and add tests.

Check List

Tests

• Unit test

Questions

Will it cause performance regression or break compatibility?

No

Do you need to update user documentation, design documentation or monitoring documentation?

No

Release note

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• CharlesCheung96
• asddongmen

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[Rustin170506]

self check

[codecov-commenter]

Codecov Report

Merging #6109 (491089b) into master (5c5c5a5) will increase coverage by 0.0382%.
The diff coverage is 71.6895%.

❗ Current head 491089b differs from pull request most recent head 5e2b39f. Consider uploading reports for the commit 5e2b39f to get more accurate results

Flag	Coverage Δ
cdc	63.2565% <79.5620%> (+0.1110%)	⬆️
dm	51.9508% <100.0000%> (+0.0306%)	⬆️
engine	62.4577% <56.9620%> (-0.0224%)	⬇️

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

@@               Coverage Diff                @@
##             master      #6109        +/-   ##
================================================
+ Coverage   57.7148%   57.7531%   +0.0382%     
================================================
  Files           699        700         +1     
  Lines         82743      82470       -273     
================================================
- Hits          47755      47629       -126     
+ Misses        30637      30507       -130     
+ Partials       4351       4334        -17     

[Rustin170506]

/merge

[ti-chi-bot]

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

Commit hash: 51192af