cmd: Make changefeed sort dir visible (#2222)

[ti-chi-bot]

This is an automated cherry-pick of #2222

What problem does this PR solve?

This PR try to revert part of the work in #1784, also fix a problem when try to set data-dir by existed changefeed information.

• sort-dir can be read but cannot be written.
• create dir temporarily when try to find best data-dir by existed changefeed information.

What is changed and how it works?

revert changefeed info struct and related read and write.

Check List

Tests

• Unit test

Code changes

Side effects

Related changes

Release note

• No release note

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[3AceShowHand]

/run-all-tests

[ti-chi-bot]

Merge canceled because a new commit is pushed.

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@ti-chi-bot: Your PR was out of date, I have automatically updated it for you.

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/run-all-tests

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