[DNM] rename resolved-ts to watermark

[zhangjinpeng87]

What problem does this PR solve?

Issue Number: Close https://github.com/tikv/tikv/issues/16708

Part of https://github.com/tikv/tikv/issues/16708

What is changed and how does it work?

Rename ResolvedTS to a understandable name Watermark.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Code changes

• Has the configuration change
• Has HTTP API interfaces changed (Don't forget to add the declarative for the new API)
• Has persistent data change

Side effects

• Possible performance regression
• Increased code complexity
• Breaking backward compatibility

Related changes

• PR to update pingcap/docs/pingcap/docs-cn:
• PR to update pingcap/tiup:
• Need to cherry-pick to the release branch

Release note

None.

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[FORMAT CHECKER NOTIFICATION]

Notice: To remove the do-not-merge/needs-linked-issue label, please provide the linked issue number on one line in the PR body, for example: Issue Number: close #123 or Issue Number: ref #456, multiple issues should use full syntax for each issue and be separated by a comma, like: Issue Number: close #123, ref #456.

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[ti-chi-bot[bot]]

@zhangjinpeng87: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
idc-jenkins-ci/build	bdc58713e90e43086683572b7aaad5e6d399b84b	link	true	/test build

Full PR test history. Your PR dashboard.

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[ti-chi-bot[bot]]

PR needs rebase.

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