puller(ticdc): always split update kv entries in sink safe mode (#11224)

[ti-chi-bot]

This is an automated cherry-pick of #11224

What problem does this PR solve?

Issue Number: close #11231

What is changed and how it works?

After introduce #10919, we choose to just split some update kv entries in puller module when changefeed starts and avoid split any update events in sink module.
This makes it possible to meet duplicate entry error during normal run and cause changefeed to restart.
Although after restart, puller can split the conflict update events and changefeed can continue to run normally. Some customer may be unhappy with this behavior if their workload has many conflict data which cause changefeed restart occasionally. So we need a workaround to avoid restart.

This pr introduce a type PullerSplitUpdateMode to describe how puller handle update kv entries. We keep all split logic unchanged as in #10919, and introduce a new behaviour:
When mysql sink is in safe mode, we set PullerSplitUpdateMode to PullerSplitUpdateModeAlways. This means to split all update kv entries in puller. So if the customer don't want changefeed to restart, they can config safe-mode to true to avoid the restart.

Check List

Tests

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

Questions

Will it cause performance regression or break compatibility?

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

Release note

None

[ti-chi-bot]

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This pull-request has been approved by: lidezhu

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