drainer: fix filter skip checkpoint problem (#1069)

[ti-chi-bot]

This is an automated cherry-pick of #1069

What problem does this PR solve?

1. When pump continuously writes binlogs, it won't write any fake binlog
2. When drainer filters dml/ddl binlogs, it won't update checkpoint using filtered binlog's commit_ts.

If we continuously write TiDB but filter most tables, drainer's checkpoint tso won't update in a long time has some bad effects:

1. make users think drainer is stuck
2. triggers drainer checkpoint not change alert
3. waste time to recover from a much former checkpoint

What is changed and how it works?

Rewrite filtered binlogs to fake binlogs (commit ts = filtered binlog's commit ts) and send to drainer.
To avoid too many fake binlogs, we only re-generate fake binlogs after AT LEAST 3 SECONDS.

Check List

Tests

• Unit test
• Integration test

Code changes

• Has exported function/method change

Side effects

• Possible performance regression

Related changes

• Need to cherry-pick to the release branch

Release note

• No release note

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• glorv
• lichunzhu

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[glorv]

@nongfushanquan PTAL, we need to merge this PR to v5.2.1.

[lichunzhu]

/merge

[ti-chi-bot]

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

Commit hash: 20ddd85

[glorv]

/run-all-tests

[purelind]

/run-all-tests