kv(ticdc): set debug level for resolved ts fallback log (#5558)

[ti-chi-bot]

This is an automated cherry-pick of #5558

What problem does this PR solve?

Issue Number: ref #4146

What is changed and how it works?

Set debug level for resolved ts fallback log in kv client.
This log is not helpful in the most of time. Any region transfer may trigger the log.

Check List

Tests

• Manual test (add detailed scripts or steps below)
  See Too many repeated logs when TiDB OOM #4146

Questions

Will it cause performance regression or break compatibility?

Do you need to update user documentation, design documentation or monitoring documentation?

Release note

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has not been approved.

To complete the pull request process, please ask the reviewers in the list to review by filling /cc @reviewer in the comment.
After your PR has acquired the required number of LGTMs, you can assign this pull request to the committer in the list by filling /assign @committer in the comment to help you merge this pull request.

The full list of commands accepted by this bot can be found here.

Reviewer can indicate their review by submitting an approval review.
Reviewer can cancel approval by submitting a request changes review.

[overvenus]

/merge

[ti-chi-bot]

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

Commit hash: a764766

[nongfushanquan]

/run-kafka-integration-test

[overvenus]

Merged by #4666.