etcd_worker: fix missed watch events caused by progress notifications (#3848)

[ti-chi-bot]

This is an automated cherry-pick of #3848

What problem does this PR solve?

Close #3750 #3815

What is changed and how it works?

• Do not use progress notifications to update the maintained watermark of the Etcd watch stream.

Check List

Tests

• Unit test
• Integration test

Related changes

• Need to cherry-pick to the release branch

Release note

Fix a bug in EtcdWorker that could hang the owner or processor.

[ti-chi-bot]

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[ti-chi-bot]

@ti-chi-bot: This cherry pick PR is for a release branch and has not yet been approved by release team.
Adding the do-not-merge/cherry-pick-not-approved label.

To merge this cherry pick, it must first be approved by the collaborators.

AFTER it has been approved by collaborators, please ping the release team in a comment to request a cherry pick review.

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[ti-chi-bot]

@ti-chi-bot: PR needs rebase.

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[VelocityLight]

This pull request is closed because it's related version has closed automatic cherry-picking.
If it's still needed, you can reopen it or just regenerate it using bot,
see:

• https://prow.tidb.io/command-help#cherrypick
• https://book.prow.tidb.net/#/plugins/cherrypicker

You can find more details at:

• https://internals.tidb.io/t/topic/785