relay/syncer: relay notifies syncer of new write to reduce sync latency (#2225)

[ti-chi-bot]

This is an automated cherry-pick of #2225

What problem does this PR solve?

• subtask 2 and 3 of relay: refactor dm-worker relay logic #2214
• fix unstable integration test case: ha_cases3(see comments below)

What is changed and how it works?

• add Listener function to relay, it notifies after writing events successfully
• add EventNotifier to local binlog reader(used by syncer), and change polling file change to waiting on write events to reduce sync latency

Check List

Tests

• Unit test

[ti-chi-bot]

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[Ehco1996]

no need to cherry pick