cmd: hide --sort-dir in changefeed command. (deprecated warning exists) (#1784)

[ti-chi-bot]

This is an automated cherry-pick of #1784

What problem does this PR solve?

Hide --sort-dir in changefeed command

What is changed and how it works?

• Hide --sort-dir in changefeed command
• Set SortDir to `json:"-"` in changefeed, so the changefeed query won't print any sort-dir which may confuse user. Note only set it to an ignore field is backward compatibility

Check List

Tests

• Unit test
• Integration test

Release note

• No release note

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• amyangfei
• leoppro

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[zier-one]

/merge

[ti-chi-bot]

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

Commit hash: fefb29c

[lonng]

/merge

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